The TSB became the first high street bank to backdate admission to its scheme for part-timers, most of them women. Its decision, which the bank admitted would cost millions of pounds, affects thousands of staff who have worked there since 1976. It follows the threat of legal action from the banking union, Bifu.
The country's industrial tribunal system, which was due to hear Bifu's case, had been swamped by more than 45,000 claims following the court ruling in October. Some union officials estimate the number of cases to be nearer 70,000.
Although some small insurance companies have already given in to union pressure, TSB is by far the biggest employer to do so. Ed Sweeney, Bifu's deputy general secretary, said: "There are about 490,000 part-timers working in the financial industry. This could cost employers significantly above £50m just in our own sector."
Bryan Freake, pensions officer for the white-collar union MSF, said agreements had been reached at General Accident to backdate rights for 300 staff to 1976. Other organisations which have also struck deals with MSF are London & Manchester, Britannia Life and NFU (Avon).
Millions of workers in other sectors, particularly the retail trade, could also be offered equal pension rights with their full-time colleagues.
However, participation in the schemes could prove too costly for many because most financial institutions have non-contributory pension schemes. Some employees would have to make substantial payments to join.
The European Court ruled in October that companies could be guilty of indirect sex discrimination if they did not allow part-time workers to join works pension schemes. Although more pension funds, including the TSB and most other banks, have started admitting part-timers since the late 1980s, people have not been able to backdate claims for benefits.
A TSB spokesman said yesterday: "The exact legal position is not yet clear and we could have waited a long time before it was resolved. We decided of our own volition to give these rights to our staff, the vast majority of whom will benefit."
Among those who will not benefit are part-timers who joined TSB after 1976 but left before December 1990, when the bank admitted all its staff into the scheme. TSB conceded this arbitrary cut-off point could still be challenged at an industrial tribunal.
No one knows which British laws will be used to decide a cut-off point for claims. The Pensions Bill, which is going through Parliament at present, is not clear on any time limit.
Industrial tribunals can decide which laws apply but a decision made by one industrial tribunal is not binding on another.