Changes to GPs' working hours have led to a huge surge in demand for ambulances, a senior health official claimed yesterday.

Bill Brackenridge, the chairman of the Scottish Ambulance Service, said increasing numbers of patients were dialling 999 when they needed medical attention because they knew their GP would not be available.

The pay and conditions deal struck with the Scottish Executive last year allowed GPs to opt out of providing emergency care outside surgery hours.

The ambulance service's annual review, which was published yesterday, showed that over the past five years there has been a huge increase in the number of emergency calls they receive, particularly in the evening.

Mr Brackenridge said he believed that the new GP contract was at least partly responsible.

He said: "It might well be that this is one of those unintended outcomes of the new GP contracts that patients now feel that if they need advice in the evening, they can't get their GP so they either telephone NHS 24 or they phone us and it looks to me like they're phoning us more often."

Mr Brackenridge also claimed the ambulance service was a "victim of its own success", which led to more and more people calling in paramedics when they were poorly.

"People do know that if they dial 999, they will get two green suits in a pretty quick space of time," he said.

Adrian Lucas, the ambulance service's chief executive, said the organisation was now carrying out research into what else lay behind the rise in demand so they can deal with it more effectively.

Nicola Sturgeon, the Health Secretary, said she wanted to see different parts of the NHS working together more effectively to ensure patients get the most appropriate type of care.

She also said that more could be done to educate the public about the best service to call upon.

Ms Sturgeon said: "It's in the interests of patients to make sure they get access to the right medical services We can always look to increase understanding and awareness of the range of out-of-hours services that are available and encourage people to access the right one, but the onus is on the service to be properly integrated."

Elsewhere, the annual review showed that the service is still failing to hit its targets for the time it takes for ambulances to get back on the road once they have dropped off a patient at hospital.

The so-called "turnaround" target is 12 minutes, but the review showed there had only been a slight improvement on last year and that ambulances at Glasgow and Edinburgh Royal Infirmaries were averaging around 22 minutes.

The review also showed that the planned nationwide inter-hospital transfer system, which would see a fleet of ambulances being used specifically to transport patients from one hospital to another, was still some way off because some health boards are concerned about the cost.

It is estimated that a national roll-out of the service would cost around £18m, but Ms Sturgeon said she was in favour of the plan.