A third of family doctor practices working to a new Government contract have stopped providing vaccinations to children.

The contract allows doctors to opt out of giving immunisations, leading to fears that parents may find it harder to get their children vaccinated against life-threatening diseases such as meningitis and measles.

Department of Health statistics, provided in a Parliamentary answer, show that last year 36.7 per cent of practices working to the General Medical Contract refused to give jabs for MMR, whooping cough, diptheria, meningitis and tetanus.

Primary care trusts (PCTs) take over responsibility for providing immunisation services when general practitioners opt out.

But critics say PCTs have many other responsibilities and are far less effective at targeting groups who most need help, such as single parents, the less well-educated and poor ethnic minority families who may have cultural or religious objections to inoculations.

There are fears that outbreaks of serious diseases could worsen as more GPs refuse to provide vaccinations.

More than 400 cases of measles have been confirmed in England and Wales this year, compared with a total of 77 last year.

Under targets introduced by Labour in 2004, doctors can earn up to £2,856 a year extra if they increase the number of children vaccinated in their area from 70 per cent to 90 per cent.

But GPs in poorer areas, where uptake is lower, have elected not to offer the service because they are unlikely to hit targets.

The Royal College of GPs sought to play down the immunisation exodus. Its chairman, Prof Mayur Lakhani, said: "The figures seem high to us and care should be taken not to over-interpret them."

He said many GP surgeries were on the Personal Medical Services contract and were excluded from the calculations. The PMS contract is negotiated with PCTs and covers more than 40 per cent of practices in England.

The Conservative shadow health secretary, Andrew Lansley, said: "It is a matter of concern that so many practices have chosen to opt out. I would have thought most GPs would see childhood immunisation as an essential part of their relationship with patients."

A Department of Health spokesman said: "Uptake has remained level for years at around 90 per cent for all childhood immunisations, bar MMR which fluctuates around 80 per cent. It is the responsibility of the PCTs to provide vaccination services and patients should be able to get the vaccinations they need regardless."