Trusts across the country are being asked to provide details of staff bonus schemes as the GMB trade union prepares for a national equal pay battle which it claims could add an extra£40m a year to the NHS pay bill.

The move follows the union's victory against Hartlepool and East Durham trust, where 200 women catering and domestic staff were excluded from a bonus scheme paid to male porters. The trust settled two days before employment tribunal hearings were due on the case, which lasted for two and a half years.

But NHS Confederation human resources chair Andrew Foster was sceptical about the implications of the Hartlepool case for the NHS. He said the government's plans to revamp the NHS pay structure, spelt out in the consultation document Agenda for Change, would ensure equality.

'This is a very specific settlement. I would be surprised if there were a large number of bonus schemes which discriminate between men and women,' he said.

'At present we don't have any way of sorting these things out other than have the GMB conducting a guerrilla war picking off individual trusts and dragging them through the courts.

'I think the settlement underlines the principle within Agenda for Change which will make sure that staff are paid for the work they do.'

The GMB has written to all NHS trusts in England and Wales asking for details of schemes similar to that in Hartlepool.

Regional officer Derek Cattell said legal action was already being taken against Carlisle Hospitals trust and is being considered at Newcastle City Health trust where negotiations are continuing.

'The GMB has requested details of bonus payment schemes for every trust in the country to ensure that this sort of discrimination does not continue.

'It may be that this exercise will prove very expensive for the NHS, but this is a lot of money that has been saved over the years by not paying equal rates to men and women,' Mr Cattell said.

'We are looking at jobs in which there are bonus schemes where males got a bonus and females did not. Trade unions have a legal right of access to this information, so if it is not forthcoming then there may have to be some legal redress.'

He added: 'There is a retrospective element to all this which can go back two years from when the claim was made - that may have implications for pensions.'

Equal value claims would also apply where trust services have been contracted out under transfer of undertakings regulations (TUPE). Department of Health lawyers are examining the implications of the Hartlepool settlement.

Unison lawyers acting for nurses at Carlisle Hospitals trust allege that its policy of calculating holiday pay at basic rates only, ignoring weekend and shift payments, breaches EU and UK law. If they are successful, nurses could receive an extra£500 a year at an annual cost to the trust of£200,000.