A poll by GP newspaper found practices are losing up to £30,000 a year from extended opening hours.
The survey, of 301 GPs, also found 27% felt relationships between partners, staff and managers had become strained since the introduction of extended hours last year.
In England, the extended hours directed enhanced service only pays practices for GPs' time, while the Welsh and Scottish governments provide extra funding for nurses.
The BMA has always argued that practice nurses and receptionists are vital for a ‘meaningful' extended hours service.
Many practices have agreed more flexible local deals with their PCTs, but the poll found just 8% have negotiated funding for practice nurse time.
Sara Richards, former chair of the RCN practice nurse association, said the government risks making practice nurse shortages worse with under-funded, ‘wearying' initiatives.
‘Any new work takes so long to negotiate and the government never seems to realise this. As soon as you get organised with one initiative, another comes along, she said.
‘There is a lack of practice nurses anyway, and in the future it will be considerably worse. We may get more nurses simply leaving practices if they feel they are being made to work long hours. This will certainly cause problems, especially for single-handed GPs.'
- Read the full version of this story in this week's Independent Nurse dated 24 August.
More news from 24 August