Advice to GPs to demand assurances in writing from primary care trusts over possible savings from practice-based commissioning could see doctors and PCT managers reach an impasse.

The British Medical Association's GPs committee has recommended to members that they do not agree to commission through PBC unless their PCT will guarantee in writing 70 per cent of any savings they may make. The ability to use savings for patient services was announced, as an incentive for GP practices, when PBC was introduced two years ago.

The GPs committee guidance says there is 'an absolute necessity for practices not to enter into any commissioning arrangements without written and signed confirmation from the PCT, in advance, that they will get their share of freed up resources at the end of the financial year, regardless of the PCT's financial situation'.

But NHS Confederation PCT network chair David Stout said the BMA's stance could cause problems for cash-strapped PCTs.

'The fact is, you can't spend money you haven't got, you have got to be realistic,' he said. 'PCTs and practice-based commissioners must live within the resources they have and use those resources more effectively but within the available money.

'PCTs and practice-based commissioners should agree on service redesign but I think the GPC's suggestion of a contract shows a real lack of trust, although I do think agreements should be documented.'

NHS Alliance PBC lead Dr David Jenner agreed that the doctors' stance could cause difficulties.

'PCTs have a duty to balance the books,' he said. 'The 70 per cent savings figure is guidance and at the end of the day a statutory duty outweighs guidance.'

A DoH spokesperson said guidance it published in November last year said it was 'imperative' for practices to be allowed to use a minimum 70 per cent of any freed up resources for reinvestment in care..

The DoH does not have figures for the proportion of commissioning carried out under PBC, but 95 per cent of practices have received an incentive payment for signing up to the scheme in principle.

BMA GPs committee chair Dr Hamish Meldrum said: 'Securing absolute clarity from the DoH on the rights of practices to, at least, 70 per cent of any savings made via PBC has been a bit like drawing blood from a stone.'