Secret payments to patients disabled by childhood vaccines are revealed today.
New figures show the Government has paid out £3.5 million to families who claim their children fell sick after jabs.
Over the years, up to 30,000 people have battled for compensation, with only a handful winning their cases.
The payouts - all made since 1997 - were revealed under the Freedom of Information Act. But ministers refuse to say which injections were involved - claiming such records are not kept.
The money was paid under a little-known government scheme for patients who have suffered adverse effects from immunisations.
Details of successful claims are never publicised - with ministers anxious not to encourage applications.
Families must convince health chiefs that the injections their children were given as part of public health programmes were directly responsible for making them seriously ill. Payouts are only made if there is overwhelming medical evidence to back the claim.
Information released to the Evening Standard shows that 917 payments have been made since the scheme was introduced in 1979. Last year, just one in every 33 claims was successful.
If that figure is typical, it suggests that since 1979, more than 30,000 people have fought for compensation for illnesses or disabilities they believe were caused by vaccines.
The revelation threatens to further undermine public confidence in the Government's child immunisation programme.
Today, parents demanded to know which vaccines had attracted most claims.
Isabella Thomas of the campaign group Jabs, said: "The public has a right to know which injections are involved. Parents should be able to see how many people believe their children were damaged by particular jabs. They can then make up their minds about whether it is worth the risk."
Under changes introduced by Labour in 1997, successful claimants receive
tax-free lump sums of £100,000. A total of 35 awards have been made since then - a £3.5 million bill.
Ministers insist the money is not "compensation" but to "ease the present and future burdens of the vaccinated person and their families".
They say they do not keep statistics about which vaccines are involved because it is too difficult to pin the blame on a specific injection.
A spokesman for the Department of Work and Pensions, which oversees the scheme, said: "It is not a requirement of the medical adviser. Indeed, this would be a difficult, if not impossible, task where several vaccinations had been administered within a short time, as is often the case."
However, at least one payment in recent years is known to have been made to the family of a child who died because of the MMR vaccination.
Parents want a public database to record the claims.
More than 1,000 families who believe their children were harmed by MMR jabs are embroiled in a lengthy court fight for compensation.
They include youngsters suffering from autism, brain damage, arthritis, bowel disease, epilepsy and immune system disorders. Some conditions are acknowledged - but rare - side effects of the controversial triple vaccine.
Many parents involved in the class action applied unsuccessfully for compensation under the Vaccine Damage Payment Scheme.