Twenty GPs in the towns of Crowborough, Lewes and Uckfield have agreed to provide medical cover to the end of 2007/8 for any patient needing a community hospital bed.
The action will keep open 14 beds at Uckfield Community Hospital that would otherwise have closed.
The deal with East Sussex Downs and Weald PCT, which has now guaranteed the beds will stay open to the end of the financial year, will save £75,000.
Dr Clarissa Fabre, a Buxted GP and GPC representative who agreed to work for free, said she discovered the beds would close when she found a member of hospital staff in tears at the end of August.
'I was shocked, and none of my colleagues knew anything about it. Patients love these hospitals and the government wants to devolve treatment to them,' she added.
GPs met the PCT and involved the local MP in the talks.
She said: 'We raised our concerns and got the impression that if we started saving money before April 2008 the PCT might be able to start spending money again.'
Dr Fabre said there was concern among colleagues nationally at the action.
A guarantee that GPs will be paid from April 2008 for their work is sought.
The four GPs at the Meads Surgery, Uckfield, have forfeited payments that brought them £23,000 last year.
Dr James Oliver, from the Meads Surgery, said GPs would like to transfer services out of secondary care to the community hospital such as top-up blood transfusions, peritoneal dialysis and administration of intravenous antibiotics. They are also looking at taking on the on-call night care at Uckfield.
He said: 'If you are the kind of GP who likes doing hospital medicine and seeing your patients through, you get the emotional reward of doing the whole job.
'But we don't want to undermine people being paid for this work. Our prime object is to keep the place open.'
GPC chairman Dr Laurence Buckman said: 'This is a remarkable piece of charity. I hope the PCT will honour its agreement to start paying them after six months.
'I hope the press and public will see what they are doing here.'
Nick Yeo, chief executive of East Sussex Downs and Weald PCT, said: 'I very much welcome the GPs' offer and their continued involvement in discussions on how medical services can best be provided in our community hospitals into the future.'
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