By Nick Triggle Health reporter, BBC News

The new contract was introduced in 2004

The two leading family doctor insurance companies, which cover nine in 10 GPs in England, dealt with nearly 300 complaints in 2006.

One of the firms has seen cases triple since a new contract started in 2004.

Patients said it showed the service had got worse and urged Gordon Brown to take action, but doctors said people were more likely to complain now.

The changes in 2004 allowed GPs to opt out of providing night and weekend care in a bid to ensure they were fresh for weekday work.

The out-of-hours experience is increasingly a source of dissatisfaction for patients Stephanie Bown, Medical Protection Society 'It didn't work for my mother'

Nine in 10 doctors took up the option, leaving it to local health bosses working for Primary Care Trusts to employ private firms or groups of independent doctors and other health staff to provide cover.

Critics have always maintained that the service has got worse with patients struggling to get through to doctors out-of-hours, while GP pay has broken through the �100,000 barrier.

And the latest figures come after Gordon Brown promised to address problems with out-of-hours care on the eve of becoming prime minister.

Many thousands of GP complaints are dealt with at a local level by the individual doctor or PCT.

The Medical Defence Union (MDU) and Medical Protection Society (MPS), which also offer legal advice, only get involved with the most serious and complex cases, such as those that involved deaths, compensation claims or issues that involve the regulatory body, the General Medical Council.

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The MPS figures show that officials started dealing with 30 new cases in the UK in 2003 - the last full year under the old system - but by 2006 that had risen to 100.

This was during a period when the overall number of cases about doctors remained steady at around 3,500.

Meanwhile, the MDU dealt with 182 complaints in England last year, up from 120 in 2002.

'Not surprising'

Stephanie Bown, of the MPS, said the new system has put doctors under a lot of pressure dealing with lots of patients "one after another".

"The out-of-hours experience is increasingly a source of dissatisfaction for patients."

Research by the MDU showed that the most common reasons for complaints were a delay or failure in diagnosis, a death and delay or failure to visit.

Michael Summers, chairman of the Patients Association, said: "These figures are worrying, but not surprising.

It does not mean the care is worse, but I do think doctors could improve their communication with patients Laurence Buckman, British Medical Association

"It is quite clear the service has got worse. Patients complain that they cannot get through and we have heard of doctors who have to travel hundreds of miles to see people.

"It was good that Gordon Brown said he would be looking at this issue and we would urge him to act straight away. Out-of-hours care needs more funding."

But Laurence Buckman, chairman of the British Medical Association's GPs committee, said: "It is a fact that patients are annoyed when they cannot see their normal doctor and I think this is more likely to make them complain about the care they receive.

"It does not mean the care is worse, but I do think doctors could improve their communication with patients. We have to remember that these people are often anxious and not well and need to feel reassured."

But a Department of Health spokesman said patient experience was "generally positive".

"The old out-of-hours system was unsustainable, placed an unacceptable burden on GPs and standards were starting to slip.

"If we had not negotiated a new contract, we risked the deterioration and indeed potential collapse of the GP service that has been at the heart of the NHS for nearly sixty years."