The Blairs and Downing Street have consistently refused to confirm whether Leo has had the vaccination despite the government??s advocacy of the MMR jab as the best and safest protection against measles, mumps and rubella.

This weekend the sources disclosed that it was only in the winter of 2001 when Leo was more than 1½ years old that he had the jab ?? after the family had been relentlessly challenged to declare publicly whether he had received it. Doctors recommend that it should be administered between the ages of 12 and 15 months.

According to the sources, the delay followed tension within the Blair household and in Downing Street, with advisers urging Blair to answer the relentless inquiries.

Many public health officials and politicians blame the prime minister??s refusal to answer questions for fuelling the panic over the safety of the triple vaccine. ??Blair certainly could have helped check the fall-off in vaccination levels by standing up and declaring that his son had been given it,?? said Ian Gibson, chairman of the Commons science and technology select committee. ??He should have demonstrated that what was good enough for the rest of the population, was good enough for his family.??

Concern about possible links between the MMR vaccine and a rising incidence of autism, the behavioural disorder, have gained currency over the past decade. However, the furore surrounding the controversial study of 12 children published in The Lancet, the medical journal, in 1998 sparked a crisis in confidence over the vaccine.

Although the research showed no connection between MMR and autism, Andrew Wakefield, the gastroenterologist who led the project, claimed at a press conference to launch the study that the combined vaccine was dangerous and parents should ask for its components to be given in two courses of three separate jabs.

The constituent vaccines were not available separately in Britain and levels of vaccine take-up have fallen as low as 53% in some areas of London, sparking fears that a serious outbreak of measles could lead to child deaths, as has happened in recent clusters of the infection in Ireland, Holland and Italy.

The prime minister is said to have been unaware initially that his son had not received the vaccine during the summer after his first birthday. According to sources close to the Blairs, it was only the growing clamour of questions over the family??s private attitude to MMR that led the prime minister to ask if Leo had been vaccinated.

Cherie Blair, who has indulged in plastic hip-reducing ??therapy pants??, acupuncture earrings to beat stress and a crystal pendant to promote calm, is known for her scepticism over many aspects of conventional medicine, including the benefits of vaccines.

She has also been influenced by her sister Lindsey, a lawyer turned homeopath, and her half-sister Lauren, who has fiercely criticised the bonus payments GPs receive for administering MMR, and declared that her daughter Alexandra would never receive it.

The lifestyle guru Carole Caplin, who once exerted great influence over Cherie Blair, claims today that ??extremely powerful forces?? consisting of ??leading figures in the medical establishment, senior civil servants and government health advisers?? have suppressed debate on the vaccine and ??discredited anyone questioning MMR??.

??At the heart of the conventional medicine system there exists a toxic mix of money, great power and arrogance,?? she says in The Mail on Sunday. ??So, when a courageous lone voice, such as Dr Andrew Wakefield, emerges from within their own ranks, the medical and health establishment see him as a traitor who must be crushed,?? she says.

One of the Blair insiders said last week: ??Maybe Leo would not have had MMR if it was not for the public pressure. But they have to practise what they preached, so Leo had to get the jab.??

At the same time a handful of politicians and selected journalists were assured that the baby had received the jab, but the information was given on the understanding that they would not report it, but merely seek to dampen the public speculation.

The failure of the Blair family to confirm Leo had been given the triple vaccine became the focus of nationwide concern among parents, many of whom hoped the prime minister??s wife would tell them what to do. ??She did not want to be a role model, a kind of first mother for Britain,?? said Linda McDougall, Cherie Blair??s biographer.

According to McDougall, the Blairs feared Leo would be used as a political tool to promote government policy. However, the pressure on the family continued and Blair was provoked in December 2002 into issuing a furious statement justifying his silence.

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