The Government’s pledge of “substantial new money”, on top of piecemeal improvements at individual schools, holds out the prospect of a lucrative business opportunity.

Yet bad advice, provided by the incompetent as well as the unscrupulous, can lead to expensive mistakes, according to the British Security Industry Association.

“One of the problems is that people are rushing out and throwing technology at the problem, without looking at how it will operate in a school,” says BSIA marketing manager Tony Makosinski.

“There are a lot of people, a local electrician maybe, saying ‘I can fit CCTV’ without thinking about who is going to look at the pictures, for example.

The BSIA will be organising a series of regional conferences for headteachers and governors this autumn with a view to producing some guidelines on school security.

It recommends that schools obtain impartial advice before making any changes. This should include discussions with police crime prevention officers and a site survey.

“Most of our members could tell you horrendous stories about people buying the wrong kit,” Mr Makosinski says.

However, changing attitudes is at least as important as introducing physical controls - and often harder to achieve.

“A lot of the time, it is about introducing discipline into a fairly indisciplined environment - like not letting visitors into the building, ” Mr Makosinski says.

“Look for something that is workable and does not require massive changes in behaviour.

“It has got to remain effective. It is no good installing something if six months later it is being ignored because it does not fit the school’s needs. ”

He suggests that gradual changes, rather than a sudden wholesale transformation, are more likely to succeed in the long-term.

One way to find a reliable firm is to look for a BS5750 kitemark. The BSIA’s 320 member companies all meet this British Standards quality assurance.