By John Pienaar BBC News political correspondent

Political debates are frequently described as "emotional" and they are frequently nothing of the kind. Synthetic rage is part of the politician's repertoire.

But the current debate about the safety of the MMR jab - touching on the risk of infant deaths and the agonising dilemma of many parents - has touched a raw nerve.

Today, Downing Street is conceding nothing to those voicing doubts about the triple vaccine.

Numbers opting for the combined jab has fallen

Number 10 condemned what it called the "media hysteria".

Today's Sun newspaper reported that Tony Blair was "wobbling" and that he had ordered a review.

That was described by Downing Street as "wrong, full stop, no equivocation, wrong."

And its attack on the Tories - without naming the party - was similarly aggressive. Mr Blair's spokesman pointed to those using this issue as a "political football".

As for the idea that separate vaccinations might be safer, Downing Street cited the evidence that the take up of jabs in Japan - where that alternative had been offered - had fallen and children had died of measles.

Evidence from overseas

The evidence on vaccinations was always kept under constant review but all the scientific research pointed to the safety of the triple MMR jab, which had been given in 500 million doses in 90 countries, the spokesman said.

The alternative of six separate injections - two visits for each disease - left children and local communities vulnerable, he added.

"Medical opinion, not political opinion, is that separate injections would result in a low take-up and experience in Japan, where for a short period they had to introduce separate injections because of a production problem, underlines that.

This will further undermine public confidence

Dr Evan Harris, Lib Dem health spokesman

"Take-up went down and children died from measles, that is a fact. People have to address the hard reality of what Japan showed."

Conservative Central Office is anxious to avoid the charge of opportunism. The party's health spokesman is again today reiterating his support for the MMR jab.

"It is a question of what does the scientific community believe is the best way forward, and that is MMR"

The prime minister's office was refusing to discuss the case for contingency planning, anxious to avoid encouraging any lack of confidence in the MMR jab in any way.

'Opportunism'

But the Tories show no sign of backing away from their demand for a re-think.

But he is urging the provision of separate vaccinations in recognition that many parents wish to exercise choice, and any vaccination is better than none.

Now, Tory headquarters has re-released a press statement from Dr Fox stating the same position and dated January 21 last year.

It won't end Labour's accusation of opportunism, but it will allow the Conservatives to claim they have taken a consistent position.

Dr Evan Harris: Supporting the government

The Liberal Democrats are siding firmly with the government. The Lib Dem health spokesman, Dr Evan Harris, has accused the Tories of "playing politics with public health".

He said: "It is the height of irresponsibility for the Tory spokesman to call for the provision of what he accepts is a less effective and less safe approach.

"This will further undermine public confidence in a vaccination programme that is both necessary and has been found, on strong scientific evidence, to be safe.

"The Tories are not fit for government and their antics on this issue suggest that Dr Fox is not fit for opposition either."

Strong words. Tony Blair will have an opportunity to add his voice to the argument in the Commons, at question time, later today.