The long-running battle over part time workers' pension rights, which could cost public and private-sector employers an estimated £10-17bn, moved a step closer to resolution last month.

In the latest development, the advocate general of the European Court of Justice in Luxembourg, senior legal adviser to the court, gave his long awaited opinion on how far part timers excluded from pension schemes will be able to backdate their claims.

The European Court held in 1994 that excluding part-time workers from occupational pension schemes breached European law on equal pay.

Under the Equal Pay Act 1970, benefits wrongly denied can be backdated only two years, but the advocate general takes the view that claims for employers' pension contributions can be dated back to 1976.

The case will now go back to the European Court, where a judgement is expected in six to nine months. The House of Lords must then decide how to proceed.