dramatic increase in measles cases brought calls last night for a public inquiry into the MMR jab.

The number of children catching the disease has quadrupled as parents shun the triple vaccination amid fears of a link to autism.

Mike Stone, chief executive of the Patients' Association, said: 'We need an inquiry the public can contribute to. People have lost confidence in the vaccination and there are so many new pieces of evidence coming forward.'

His call was backed by experts in the field. Virologist Dr David Tyrell warned that falling vaccination rates were bringing a serious risk of epidemics and said: 'The situation is very unsatisfactory.'

Consultant paediatrician Dr Damitha Ratnasinghe of the West Middlesex Hospital said: 'A public inquiry would be the very best thing to do. Confidence in MMR cannot be re-established by simply forcing people to accept triple vaccinations.

'It's not so long since BSE and the British public think there is now a cover-up on MMR.'

The figures from the Public Health Laboratory Service show there were 126 cases of measles in England and Wales in the first three months of this year, compared to only 32 in the last quarter of 2001.

The figure - a five-year high - comes only days after research suggested that one in every 1,500 injections with the combined jab could trigger autism.

Vaccination rates have fallen from an average of 93 per cent to 84 per cent nationally and as low as 73 per cent in parts of London, a level which carries serious risks of a major epidemic. Of this year's cases, 91 come from London.

More than 100,000 two-year- olds have not had the jab, and experts believe only a public inquiry can restore confidence in it.

Jackie Fletcher, of the campaign group JABs, said an inquiry was long overdue. She added: 'So many parents are concerned and we have more than 2,000 families with children we say have been damaged by MMR. More studies are questioning the safety of MMR, yet the Government insists it is safe.'

Parental concern over MMR - measles, mumps and rubella - has grown since Tony Blair refused to say whether or not his son Leo had had the triple jab. His silence fuelled speculation that Leo had received single jabs or had not been vaccinated at all.

Many parents want single vaccines against the three diseases but the Government has refused to offer them on the NHS.

The Chief Medical Officer, Sir Liam Donaldson, fears that some parents would fail to complete the full course, putting children at greater risk. Last week, the Government was accused of 'bully-boy' tactics after it emerged that it is limiting the number of single vaccines reaching parents.

Department of Health officials ordered a supplier of rubella vaccinations to slash the number it makes available to a private clinic which has inoculated more than 30,000 children with single jabs.

The directive to Essex-based Farillon was aimed at preventing the London clinic Direct Health 2000 getting more than 100 jabs a month.

Critics said the move was a clear attempt to force parents back to the triple injection.

The difficulty of obtaining single jabs here - many clinics are booked up - has led some parents to take their children to doctors in Belgium and France, paying upwards of £180 for the return trip.

A single measles injection costs £15 in France, and if children have this vaccination abroad, they are entitled to the other two free on the NHS.

The Public Health Laboratory Service said the main reason for this year's high was an outbreak in South London which had since 'died away'.

But disease experts say general immunity levels of 95 per cent are necessary to protect the population fully.

Virologist Dr Tyrell, who spent more than 20 years studying infectious diseases for the Medical Research Council, said there was a 'real possibility' of an outbreak affecting thousands of children if vaccination levels dropped a further 8-10 per cent.

He said: 'If you get people crowded together as you do in a city, and you don't have a high proportion of them vaccinated, there is a very good chance you will get epidemics.

'If you let it go down to 75 per cent you will have massive epidemics because a quarter of children will be likely to get it, in the same way epidemics came back after people stopped taking the whooping cough vaccine.

'If you want to avoid an epidemic situation, you have to get nearly everybody immunised.'

There have already been more confirmed cases of measles in the first quarter of this year than in any full year since 1997, itself a freak due to a string of outbreaks at schools where parents refused the jab on ethical grounds.

There were 74 cases in the whole of last year, 100 in 2000, 94 in 1999 and 56 in 1998.

About one child in 15 develops complications from catching measles. These can include inflammation of the brain, fits and, in about one in every 2,500 to 5,000 cases, death.

Concern over MMR and autism first emerged in 1998, when British researcher Dr Andrew Wakefield diagnosed a bowel disease in autistic children which has been linked to MMR.

U.S. studies have since appeared to back up his findings. Last week Dr Arthur Krigsman, a paediatric gastroenterologist from New York University, told a Congressional committee on autism that he had found an identical pattern of inflammatory bowel disease in 90 per cent of his young autistic patients.

At the same time, Paul Shattock, director of Sunderland's University's Autism Research Unit, revealed that he had found abnormalities in urine samples from autistic children whose parents believe they were affected by MMR.

He said his results suggested that the vaccine is responsible for ten per cent of autism, a rate of one case per 1,500 jabs.

The Department of Health, however, insists that MMR is the safest way to protect children and there is no firm evidence of links to autism or bowel disease. A spokesman said it was keeping new evidence under review.