The NHS is probably the biggest employer affected by the House of Lords ruling last month in Preston v Wolverhampton Healthcare NHS trust, the case over part-time workers' pension rights. The Lords confirmed that present or past part-timers who were denied the right to belong to an employer's pension scheme are entitled to backdate their retrospective membership of the scheme to 1976.

But the ruling also established that only those who made claims within six months of leaving employment could take advantage of the right.

The judgement raises questions about those who have had a break in their employment. The Lords ruled that claims could be made up to six months after the end of a 'stable employment relationship', which could include a series of regular short-term contracts.

The future financial impact on the NHS is still unknown.

Unison, the public service union, thinks tens of thousands of employees and ex-employees will be affected.

They will have to find the money to pay their own backdated employees' contributions into the scheme. This 'payback' could be funded by loans or from the lump sum to which they will be entitled under the pension scheme.

The issues will have to be thrashed out in negotiations between unions and the NHS pensions agency. Unless agreements can be reached, cases are expected to go to employment tribunals in blocks.