But new guidance from the Department for Education and Skills makes it clear that benefits payable on any additional pensionable service earned after the changes come into effect will be reduced, if teachers decide to leave at 60 rather than 65.

Government plans to require public-sector workers to work additional years to receive their full pension have caused uproar among teachers. A Department for Work and Pensions paper proposes all new teachers will have to stay on until 65 to qualify for a full pension. Currently, only 500 teachers a year work until then, and unions have said the move will do nothing to help recruit, retain and motivate staff.

But David Miliband, school standards minister, told the Commons education select committee: “I think there is a lot of erroneous information out there. The ordinary teacher sitting in the staffroom might think you are not going to be able to retire until you are 65. If you have got 20 years of credits and want to retire at 60, you can take it. There is no question of robbing teachers of what they are entitled to or have built up.”

However, the DfES guidance cites the example of a 45-year-old with 20 years’ service when the changes come into effect. If he or she quits at 60, the proportion of pension based on the last 15 years’ service would be reduced to take account of it being paid before 65.

Eamonn O’Kane, general secretary of the National Association of Schoolmasters Union of Women Teachers, said: “This guidance confirms our fears, and will meet with intense opposition. Traditionally, public-sector workers have been paid less but have had better pension provision. If that is weakened, it will be disastrous for recruitment and retention.”