Phone for a GP this weekend in Northumberland or Tyneside and there is a fair chance you will be seen by a practitioner from Germany.

On some occasions now a third of the 40 or so doctors on duty covering 1.2 million patients in the north-east region have just stepped off the plane from Germany.

And the situation is repeated across the country. From Cornwall to the Scottish borders, doctors, not only from Germany but also from Spain, the Netherlands, and eastern Europe, are arriving every Friday night - to possibly make £2,000 over a single weekend.

The influx of German doctors, they have dubbed it "island hopping", is one of the most dramatic indications of the growing problems with the out-of-hours system, according to GPs. A fundamental change in the way the services are organised has led to a dearth of local GPs for the most urgent cases, they say.

The system was altered last April. Family doctors were given the chance to pass on the responsibility for night-time and weekend duties to NHS primary care trusts. Most GPs leapt at the offer. They stood to lose £6,000 a year gross but saw that they could do out-of-hours work on an ad-hoc basis at up to £100 an hour and recoup their loss within seven or eight nights.

Some doctors are doing just that, making up the shortfall and perhaps a little more and keeping their nights and weekends undisturbed. Others, including many of the older GPs who are already financially comfortable, have decided not to do any extra shifts.

Organisations such as the British Medical Association claim these moves have made the shortage of GPs worse. Additionally, the primary care trusts are allowed to provide the out-of-hours services in-house or contract them out to private companies, other health trusts or cooperatives.

The fear now is that many of the trusts, realising that the out-of-hours service is a hugely expensive business, may be tempted to cut corners. Trusts in one region have already tried to dispense with the services of doctors at night and use only nurses.

Some doctors who work the out-of-hours shifts claim they are being expected to cover huge areas, especially in rural districts.

Doctors are also complaining that they are not getting enough information from the trusts about how the new out-of-hours system is working. The Freedom of Information Act is being used to try to force some trusts to provide details of complaints made about the system. Even some of those doctors who wanted to continue to do regular out-of-hours shifts are beginning to think twice because of how the system is working out.

The government insists that out-of-hours services are well-funded; about £316m in total was available last year. It claims the system is better because the trusts have to meet a national standard.

The Department of Health also says it has no problem with the increase in the numbers of foreign doctors.

But some GPs are not so sure. Nigel Watson, who is a GP working in the New Forest, and also the chief executive of Wessex Local Medical Committees, said: "Some of them are very good but there are questions about whether they understand the system, how it all works. There've been concerns about one or two."

George Rae, a GP in the north-east of England, said language could be a problem but it was particularly crucial for patient and doctor to understand one another during an out-of-hours consultation because the GP might have to quickly understand the medical history. Dr Rae said: "We've got to get the communication spot on."

Pat McGrann, a GP in North Yorkshire, said: "I believe that the only people with the experience to run out-of-hours services are GPs. The system needs to be rethought"

Sonja Michalke, a German doctor who has worked in Suffolk, said that weekend cover in Britain remained a lucrative option. She saved on accommodation costs by staying with friends in Cambridge, and booked cheap flights between Berlin and Stansted airport several months in advance. "I have to pay my flight. But once I'm in Suffolk I get 55p a mile mileage up to £40 a day. On an average weekend I earn £1,200."

But the exodus of well-qualified doctors to the UK creates problems for Germany, health officials in Berlin said.

There is an acute shortage of doctors in east Germany, Hans-Jörg Freese, the spokesman of the German Medical Association, told the Guardian. It was a problem likely to worsen when the large number of German doctors already in their 50s retired.

Eric Peacock, chief executive of Northern Doctors Urgent Care, which is charge of the out-of-hours service in Northumberland and Tyneside, said that he had had to bring in German doctors because local GPs did not want to do certain shifts such as Friday and Saturday nights

"I would like to employ local doctors but I just can't get them," he said.