Local government unions are already negotiating with employers and the Department of the Environment on changes to their pension schemes that would enable unmarried partners of deceased contributors to claim on their partner’s pension under the Teachers’ Superannuation Scheme.

At present widows and widowers get a maximum (depending on exactly when the teacher involved joined the scheme) of half their spouse’s pension when the spouse dies, while children get another quarter. Unmarried partners, and the children of unmarried partners, get nothing.

The argument is that present pension rules are out of touch with social realities in the 1990s, where official figures show many more children being born out of wedlock but with parents living at the same address - an indication that many more people are undertaking long-term relationships without going through a marriage ceremony.

Pension funds should reflect the fact that most long-term but unmarried partnerships, which often include joint mortgages and joint bank accounts even if they don’t include children, involve just as much commitment, dependency and responsibility as a marriage, campaigners say.

Barry Fawcett, assistant secretary for pensions and salaries at the National Union of Teachers, said that the Teachers’ Pensions Working Party, which includes all the teaching unions, agreed just before Christmas to approach ministers with a call to extend the pension rights to teachers’ unmarried partners. The working party hopes to meet the Department for Education and Employment before Easter to discuss it.

Mr Fawcett said: “Social attitudes have changed. A lot of people now live together and it is time to campaign for a change to pension schemes to reflect this.”

Unmarried partners of contributors to the teachers’ pension scheme would almost certainly need to be nominated by their partner to have any rights to their pension after their death.

Sources say that union negotiations have deliberately not raised the issue of whether any granting of “partnership pension rights” should include same-sex partnerships, for fear of “the Daily Mail effect” - a right-wing uproar which might sink the whole campaign.

The most important hurdle, however, is likely to be the Treasury, which is likely to try to block any scheme that would increase public spending. Local government unions have been told that their own campaign to improve pensions for partners would add about Pounds 274 million to local government costs.

Campaigners say the DFEE is “a bit reluctant to make changes which might require them to seek approval from the Treasury”.

But Brian Clegg, assistant general secretary in charge of salaries and pensions at the National Association of Schoolmasters Union of Women Teachers, said that funding for the TSS had been set up originally in the expectation that most people would get married and be survived by a widow or widower. Social changes and the growth of unmarried partnerships in the past 10 years had therefore actually brought a saving, he said, and including unmarried partners in the scheme with the same rights as married partners would therefore cost “less than half a per cent”.

The TUC has estimated that about 220,000 public sector workers are unmarried but in long-term relationships with live-in partners. Many private companies are already starting to change their pension rules to include unmarried partners, Mr Clegg said, and trustees for the pension funds of newly-privatised parts of the Civil Service generally did the same.

“We have moved in the past three years from there being little interest in this to working out the details. It’s now all down to political will,” he said.