By Daniel Martin and David Derbyshire
The cervical cancer vaccination programme was last night branded a 'public health experiment' by a senior researcher who helped develop the drug.
Dr Diane Harper - one of the world's leading cervical cancer experts - said health officials and drug firm bosses were exaggerating the jab's benefits.
And she claimed parents were not being properly warned about the 'small but potentially adverse' risks of Cervarix and other vaccines.
But health officials, cancer charities and scientific experts all insist the programme is safe and urged parents and schools not to panic.
Dr Harper's comments follow the death of 14-year-old Natalie Morton, who collapsed an hour after receiving the jab at school on Monday.
Initial post mortem results have suggested that her death was caused by a rare and serious illness - rather than the cancer vaccine.
Under the Government's cervical cancer programme, Cervarix is being offered to girls between 12 and 18.
It works against two strains of HPV - a sexually transmitted virus that causes 70 per cent of cervical cancer cases.
Yesterday the Department of Health said it had 'great confidence' in the safety of its cervical cancer vaccination programme.
'We have been clear all along that there is no reason to suspend HPV immunisation - the programme against cervical cancer continues today,' a spokesman said.
'We have one of the most successful immunisation programmes in the world and have great confidence in the safety of them.
'Young girls can continue to protect themselves against cervical cancer by having this vaccine.' But Dr Harper, of the University of Missouri-Kansas, who was involved in the clinical trials of Cervarix, believes it should have been tested for another four years before being introduced in Britain.
Patient trials have only been running for seven and a half years - not long enough to show whether it continues protecting women into their late 20s and 30s, she said.
'It is a public health experiment,' she said. No efficacy studies have been done to measure the effect of the vaccine on girls under 15, she added.
'Parents consenting to HPV vaccination must be told that the duration of the vaccine is unknown, and that it is entirely possible that the initial vaccination series will only postpone, not prevent, future cervical cancers in their daughter,' Dr Harper said.
Around one million girls have been given the vaccine. There have been 4,657 reports of suspected adverse reactions - including sore arms, dizziness and swelling.
Although the drug is safe for the majority of women, there are very rare 'real dangers' - including the risk of brain damage, paralysis and death, Dr Harper said.
Even if the jab is only dangerous for one person in a million, women should be told the risks, she said.
She also believes the benefits of the vaccine as a 'cure' are being exaggerated. The jab does not prevent 30 per cent of cervical cancers - which means women will still need to be screened for pre-cancerous lesions.
Dr Harper helped develop the HPV vaccine which is produced as Cervarix - the GlaxoSmithKline product distributed by the NHS - and Gardasil which is produced by Merck and distributed in the U.S.
A Department of Health spokesman said: 'It is wrong to suggest the benefits are exaggerated. Ninety nine per cent of cervical cancer cases are caused by HPV and the vaccine will protect against about 70 per cent of them.
'The evidence is that the vaccine is very safe. And long-term follow up studies have shown that it offers extremely high levels of protection that continue to last.'
An initial post mortem showed the vaccine was 'unlikely' to have caused the death of Natalie Morton as she had a rare and grave underlying health problem, which was unknown to her family.
Stepfather Andrew Bullock said Natalie, who attended Blue Coat CofE School, in Coventry, had been 'poorly for some time'.
She had been to see her GP several times and investigations into a mystery illness had been under way, he said.
How Britain went for the £18m cheaper option
Britain's decision to go against the rest of the Western world and opt for the Cervarix vaccine was made to save money, health charities claim.
They said the decision condemned thousands of young women to an unpleasant sexual infection from which they would have been protected had ministers chosen the rival vaccine, Gardasil.
The U.S. and every single major western European country went for Gardasil, which protects against more strains of HPV, the sexual infection which can cause cervical cancer.
It is understood that Britain chose Cervarix after the Health Protection Agency advised that it would save more than £18million a year.
There is no suggestion that Gardasil is any safer than Cervarix. In fact there have been 30 deaths following reported adverse reactions to Gardasil in the U.S., plus a number in Germany and Austria.
But charities pointed out the extra strains of HPV that Gardasil protects against would have prevented thousands from catching genital warts - an infection on the rise, especially among the young.
They said the money saved will be outweighed by the £22million the NHS spends every year treating genital warts.
'Our concern is that we didn't pick the right vaccine in the UK,' said Lisa Power, of the Terrence Higgins Trust sexual health charity. 'We felt that Gardasil was more effective against more things.
'HPV may not be fatal, but it is very unpleasant and it is on the rise. In 2008 there were 92,525 new cases of genital warts. That's very expensive to treat, as well as leaving 92,525 very unhappy people.'
GlaxoSmithKline, which makes Cervarix, claims its vaccine lasts longer than Gardasil, meaning there is less chance of a booster being needed later in life.