Diana was an experienced head of department. She joined the school after a period working abroad and came across as well-qualified, enthusiastic and loyal. But not long after her arrival, stories about her conduct began to do the rounds, soon reaching the ears of the headteacher.

She did not mark work; she managed to avoid going on duty; her classroom management was poor. In fact, she was accused of reading The Guardian in a cupboard next to her classroom while pupils worked unsupervised.

Alarmed at the reports from both pupils and fellow teachers, the headteacher confronted Diana. It was a heated exchange. Shortly afterwards, a series of anonymous emails levelling accusations at the head and other teachers began to circulate around the school and local authority. It was clear that Diana was not going to go quietly.

Investigation by the school’s network manager established that Diana was the source of the emails. She decided to resign, but only after enlisting her union in a prolonged fight that eventually foundered on the weight of evidence against her. The network search also uncovered another teacher’s predilection for Asian porn and a third’s interest in bomb-making. Both teachers resigned and were reported to police, but would have escaped suspicion if an investigation had not been launched in the first place.

Ever since Chris Woodhead claimed that there were 15,000 incompetent teachers in England when he became chief inspector of schools in the 1990s, debate has raged on the difficulties of removing those who don’t come up to scratch. While his successors have been more circumspect about numbers, in presenting Ofsted’s last annual report before this year’s general election Christine Gilbert, the present incumbent, claimed that there was a “stubborn core” of inadequate teaching.

While the consequences at an individual class level are acute, these are magnified when the teacher in question is a member of middle management. These “bed blockers” may have been promoted in an enthusiastic phase of their career, or because they stuck around for a while, but are now coasting and preventing other teachers getting promoted.

This situation is, if not familiar, at least recognisable to Diana’s headteacher, Trevor Averre-Beeson. Dealing with incompetent teachers, and incompetent heads of department, has been an occupational hazard during his 14 years of headship.

“It is part and parcel of a headteacher’s job,” says Mr Averre-Beeson, former head of three London secondaries and now director of Lilac Sky Schools, an education consultancy. “I would be very surprised if there was a school in the country that didn’t have one or two teachers who were struggling.”

But not everyone believes this system is working effectively. Joan McVittie, headteacher at Woodside High School in north London, has raised the difficulties of removing poor teachers in meetings with Schools Secretary Ed Balls.

“It is too long-winded and very onerous. Children only have one chance and the process really needs to be sped up,” she says. “I always ask myself how long I would want this person teaching my daughter. If you have a poor teacher for 18 months then that is your GCSE gone.”

Mrs McVittie says that the problem of poor middle managers is one she has encountered in most of her schools. “If somebody has been promoted beyond their capability they block promotion for younger, brighter ones,” she explains.

Ian Bruce, headteacher at Rosemellin Primary in Camborne, Cornwall, acknowledges that middle leaders can be a plug in the system. “It is frustrating for the teachers coming through,” he says.

But it could soon be harder for poor teachers to hide. Ofsted’s new inspection framework will see a doubling in the number of lessons inspected and Mrs Gilbert has promised that substandard teachers face a crackdown.

While Vernon Coaker, schools minister, has spoken out against measures that would make it easier to sack underperforming teachers, there are signs of a new ruthlessness in schools.

Academies with responsibility for their own employment practices, and the gradual embrace of performance management, could herald an age of austerity for underperforming teachers. On top of this, the Government’s proposed Licence to Teach will provide a five-yearly check on quality, and a possible exit route to those who fail to meet the standards.

Mr Bruce, also south west England representative for the National Association of Head Teachers, says the process is such that heads are reluctant to embark on it unless necessary. “You are only going to do it when there is a real issue,” he says.

Those who face dismissal are the extreme end of the spectrum. For most struggling teachers, coaching and support can be highly effective. “If support and training is done properly, over a period of three months or so, the majority of people will step up,” says Mr Averre-Beeson. Where this doesn’t work, he says there are tried and tested procedures for dismissing someone on the grounds of incompetence.

One of the problems school leaders encounter is heads of department who have been promoted beyond their abilities, says Richard Bird, legal adviser to the Association of School and College Leaders and himself a former head. “They have risen to the level of their own incompetence,” he says.

A private sector firm would probably fire them and prepare to take a hit at an employment tribunal, he says, but the need to account for public money and aspirations to higher ethical standards mean schools are reluctant to go down this path.

Redundancies or reorganisations provide opportunities for heads to take a teacher’s contribution to the school into account. Quality of work is a legitimate criterion in deciding who should go and who should stay, but needs to be based on objective evidence.

Teachers should not lose their jobs because the head doesn’t like the colour of their eyes or their hair, Mr Bird adds.

Redundancy and reorganisation can also unsettle valued staff. An alternative, perhaps more frequently used in the past, is moving teachers into jobs where they can do less damage. Mr Bird recalls one colleague given responsibility for the school site to take him out of the classroom, while Mrs McVittie cites the role of head of careers as a popular destination for struggling teachers in the past. Schools increasingly fill these jobs with non-teacher specialists, however, closing off this option to many heads.

Sometimes it’s a question of the right person in the wrong job. One former head recalls a head of sixth form who was a “disaster”, lacking any vision, energy and leadership. When he was put in charge of examinations, however, he found his niche and became a font of wisdom.

School leaders should also consider whether there are good reasons for a teacher losing motivation, says Mr Bird. Heads of foreign languages, history and geography, who have seen their subjects steadily downgraded in recent years, could be forgiven for feeling disillusioned, he adds.

“There are people who have been systematically ground down and it may be that decent leadership will turn them into valuable members of staff,” he says.

Where teachers do not measure up, they can be taken through a capability procedure. This normally involves an informal, and if required a formal, component. Providing appropriate help for teachers to meet their job requirements is a key part of this process, says Alan McMurdo, principal of the Thomas Deacon Academy in Peterborough. This should be seen as a supportive rather than a punitive step, he adds.

This could involve buddying up with another teacher, watching another teacher at work, visiting neighbouring schools or attending courses. “This support phase is absolutely bespoke to address the issues that have been raised,” Dr McMurdo says. “The vast majority of colleagues who have been through that process respond very positively.”

Dealing effectively with teachers who are not up to scratch comes down to a proper use of performance management, says Mr Bird. “When you consider someone’s performance, you have to insist that the qualities you need are there,” he says.

Where this can fall down, he says, is an enduring belief that all teachers are equal and middle managers are only there to co-ordinate exam entries. For some heads, the award of a Teaching and Learning Responsibility (TLR) allowance is a way of rewarding good teachers without expecting anything in return. “I’m staggered at how slow schools have been to accept the idea that if you are given a TLR you are expected to lead,” he says.

Teachers who have been given management roles should be measured against the leadership requirements of the job, he adds. But while a classroom teacher can be measured through examination results and lesson observations, ability to lead and inspire is harder to pin down.

Mrs McVittie has used the TLR system as a basis for reorganisations at two schools. “It has been very helpful in terms of redistributing responsibility,” she says. “We were able to identify what jobs we actually needed rather than what we had inherited.”

She recognises that teachers are entitled to a due process but feels the existing system is too drawn-out and provides too many opportunities for delay. “If Ofsted comes in and my results aren’t as good as they should be, nobody gives me due process. I would be out on my ear pretty quickly,” she says.

In theory, performance management is a straightforward process, involving collecting and presenting evidence. Even so, Mr Bird knows of heads who have waited for 10 or more years, hoping a particular head of department will leave but unable to find enough evidence that they are not up to the job.

The formal part of the procedure is supposed to take about two terms. But there can be hitches.

“A major issue with marginal performers is when you start to monitor them they go off sick,” says Mrs McVittie. The process then becomes one of managing long-term sick leave, rather than performance, although the end result is often the same.

Prolonged sickness absence is a familiar bugbear for heads. When Mrs McVittie arrived at Woodside there was a significant number of staff who had upwards of 30 days off sick a year and some with 60 to 70 days absence the previous year, out of a school year of 190 days.

Her response was to set targets, telling teachers they would have to appear in front of the governors if they had more than eight days off sick a year, the national average. But she says the ability of a teacher to stretch the process out proves a hindrance to removing those who are not doing their job. “It is stacked in favour of the employee, not the children,” she says.

Kevin Harcombe, headteacher at Redlands Primary in Fareham, Hampshire, says going off sick is a familiar response to capability procedures. “They go off sick for six months, come back and then go off sick again,” he says. “It can reach the point where the HR department will suggest the governing body moves to dismissal anyway.”

Like Mrs McVittie, he believes the process for sacking staff on grounds of incompetence is long-winded, although he is cautious about whether it should be sped up. “I’ve got reservations about making it shorter and sharper because I know there are vindictive bosses out there and that could open the door to them,” he says. “It’s a tough one because there needs to be safeguards, but I would like it sped up, with safeguards.”

Instead of two terms, it can take up to two years to dismiss an underperforming teacher, says Mr Bruce. “It is a time-consuming process,” he adds. But he acknowledges that it would be problematic to make it shorter.

“The whole point of capability is to improve people. It is important that they are given a fair chance because at the end of it they could lose their job.”

To avoid dismissal, some teachers opt to leave voluntarily, either to join another school or a supply agency. This would chime with Dr McMurdo’s experience that few schools have the “stubborn core” of poor teachers that Mrs Gilbert cited in her annual report.

“I have a feeling that what the chief inspector is talking about is a group of people who perhaps move around the system,” he says. “It is not as if heads have a clump of these obdurate inadequate teachers that they are not doing anything about.

“What happens is heads do something about it and they leave. It is a bit like pushing the ruck around the carpet.”

A less kind image is the American “Dance of the Lemons”, used to refer to inadequate teachers being passed from school to school, often accompanied by a good reference. The problem with this tactic is that it usually only works once. It can also scupper the prospects of good teachers who want to make the same move, not to mention being unethical.

As a result it is seldom employed. But seldom does not mean never. “I have had it happen to me,” says Mrs McVittie.

“I have had references for people saying they had good attendance but when they arrived they didn’t have good attendance and when I made inquiries I discovered they did not at their last school either.”

When references turn out to be misleading, she says she always goes back to the head concerned to complain, and never uses the tactic herself. “I have always given an honest reference, even when a member of staff has left under a compromise agreement.”

One tactic deployed by teachers who are in difficulties is to try to cover up their weaknesses with confusion, or else take an aggressive approach to challenge. Dubbed “internal terrorists” by Mr Averre-Beeson, they can have a destabilising effect on a school.

He cites the case of a member of the senior leadership team at one of his schools. She undermined his position with junior staff, called the fire brigade to test fire drills without telling him, and could never be contacted when it was her turn to be on call - claiming later she was looking for truants on the school field.

When confronted she denied knowledge of anything untoward. Eventually Mr Averre-Beeson took her to a disciplinary in front of the governors over the way she dealt with a pupil, but lost.

The teacher then lodged a grievance against him, and it was only when it emerged she had lied on her original application form that she decided to take early retirement.

Local authority human resources departments have in the past acted as something of a break on heads wanting to remove poor teachers. “They always err on the side of caution,” says Mr Harcombe.

But as more academies open, each with responsibility for their own employment policies, there may be a change in culture on the way. Perhaps an even more significant shift is occurring as performance management becomes embedded.

“Heads are increasingly willing to tackle the problem,” says Mrs McVittie. “I do think there are some people where you wonder why they came into teaching in the first place. Somebody really should have advised them that if they really didn’t like children then teaching wasn’t the best option.”

For teachers who are underperforming, there may be few regrets over their departure. While no one would suggest dismissing them would be doing them a favour, it could be the best thing for the children.

“There are people who are ill-suited to this particular profession and they need help to exit it,” says Mr Harcombe. “You have to keep in mind that it is for the benefit of the children.”