Parents are being urged to give their children the measles, mumps and rubella jab before the start of the new school year after an unprecedented surge of measles cases was recorded over the summer holidays.

Experts fear that hundreds of thousands of children returning to school as early as next week may cause the highly infectious disease to spread. Despite this the Government has ordered no extra stocks of the MMR vaccine and doctors may run out if they face a sudden rise in demand, The Times has learnt.

The Health Protection Agency (HPA) said that the number of confirmed cases of measles in children had more than trebled over recent months and was far higher than would normally be expected for this time of year.

By June 10 only 136 cases of measles had been confirmed. But just over 11 weeks later this number has risen to 480, with new cases being detected every day, the HPA said. This compares with 756 cases recorded during the whole of 2006 – the highest year on record.

Measles, which can be life threatening or cause severe disabilities, is most common among children aged 1 to 4 who have not been immunised, but can strike older children and adults, too.

It was difficult to explain the large increase this year, the HPA said, but parents not vaccinating their children and a lower uptake of a second MMR “booster” dose are thought to be key factors. The triple vaccine has proved highly controversial in recent years over unfounded concerns that it may be linked to autism. The study that first sparked fears about its safety is currently being scrutinised in a hearing by the General Medical Council, the medical watchdog. Andrew Wakefield and two co-authors of his research are currently appearing before the GMC on charges of serious professional misconduct.

MMR coverage began to drop in the late 1990s, though uptake is rising slowly again. The latest figures show that 88 per cent of British children begin school having had one dose of MMR.

But only three quarters of them have the full protection afforded by both doses. Until that figure is far higher, health officials say people should not assume that their children are safe from measles.

The latest data, for January to March 2007, showed particularly high numbers of measles cases in London and southeast England, East Anglia and Yorkshire and Humberside.

Mary Ramsay, a consultant epidemiologist at the HPA, said yesterday: “We’ve been very worried because the cases have stayed up over the summer holidays. This means it is crucial that children are fully immunised with two doses of MMR before they return to school.”

In previous decades, measles could cause an average of 20 deaths a year. Officials are nervous that the numbers could creep up again after gaps in vaccination coverage. “Although the numbers are still small, compared to the history of measles, we’re always worried about measles because very rarely it can kill,” Dr Ramsay added. “We hadn’t had any deaths from measles since the early 1990s, but unfortunately we had one death last year and we don’t want any more.

“Measles is a highly infectious and dangerous illness and, as there is increased close contact in schools, it can spread easily.”

Along with buying school uniforms and other preparations, “parents should think about adding the MMR vaccine to their back to school ‘to do’ list”, she added. “It is never too late to get vaccinated.”

But Laurence Buckman, chairman of the British Medical Association’s GPs’ committee, said that many doctors had not been warned to prepare for a sudden demand and could run out of supplies. “GPs will only have ordered as much vaccine as they would typically use at this time of year, so there may not be enough to satisfy a surge in demand,” he said. “Doctors and nurses will do their best, but at this short notice, they will not be able to run any extra clinics on the weekend and when they run out of supplies there is not much they can do.”

Doctors’ surgeries at Hackney, East London, are dealing with the effect of reduced levels of vaccination, with more than 120 measles cases in the past three months. Most of those were in children under 5 who had not been immunised.

Michael Fitzpatrick, a GP in the borough, said that he was disappointed but not surprised by the latest figures: “Scepticism about the MMR vaccine results in outbreaks of measles like this,” he said. “This was inevitable and I think the only surprise is this hasn’t happened earlier, and on a bigger scale.”

A spokeswoman for the Department of Health said that no extra stocks had been ordered, but added that supplies could be distributed to doctors with a day’s notice. “Vaccines are delivered to GP surgeries on a weekly basis. If GPs need additional supplies of MMR to meet demand, these can be ordered and then delivered within 24 hours. We currently have good stock levels of MMR.”