A Warwick Medical School study, looking at patient numbers at hospitals in Birmingham and Solihull, found the numbers of A&E patients had increased.

GPs were given the chance to opt out of the out-of-hours medical care in 2004. Primary Care Trusts took over instead.

A study spokesman said the findings could be replicated nationwide.

Professor Matthew Cooke, who led the study, said it focused on patients attending Birmingham Heartlands Hospital and Solihull Hospital, run by the Heart of England NHS Trust.

Respiratory problems

Since October 2004 out-of-hours A&E attendances had increased by 27%.

There was a 9% increase in self-referrals while the number of people wanting to be treated for minor conditions, which could be looked after by a GP, went up by 51%.

One of the biggest increases involved parents bringing in children with respiratory problems.

The study made it clear that even though the two hospitals faced increased pressure they were well-equipped to cope.

At Heartlands Hospital, a GPs' out-of-hours service works alongside an A&E service.

'Working together'

At Solihull, the two services are based in the same department.

Professor Cooke, who works for the NHS Trust, said: "By working together, primary care and the emergency department can ensure that all patients are seen by the most appropriate clinician."

A Department of Health spokesman agreed there had been a rise in attendances, but said there was no evidence to suggest it was caused by changes to the out-of-hours arrangements.

"The start of the current trend in A&E attendances pre-dates the changes to out-of-hours arrangements by a full year," he said.

GPs had been sub-contracting evening and weekend work since the mid-1990s, he added.