Approached in a supermarket by a voter asking about Birt, Prescott batted the inquiry aside by saying: “John who? First of all, let’s dismiss John bloody Birt.”

Baron Birt of Liverpool, as he is more properly known, was ennobled under Labour and is a former director-general of the BBC. At present he is strategy adviser to the prime minister.

This, however, clearly does not impress Prescott, who continued to give “bloody Birt” a good thumping.

“He might walk in and out of bloody No 10, he might whisper in his (Blair’s) ears.

“There are thousands of advisers like him. He obviously thinks he is a bit more important. That is what advisers do but they don’t make decisions.”

Prescott’s most notable decision in recent elections was to slug a voter when confronted during campaigning in 2001.

Yesterday’s outburst is remarkable considering Birt’s closeness to Blair. From his office in 10 Downing Street, Birt has been asked to develop a range of strategies for government and has ready access to the prime minister.

He has reportedly been considering plans for a new generation of nuclear power stations — which was what caused Prescott to go into meltdown when asked about it.

Birt is known to covet the job of minister at the Cabinet Office — the so-called minister for meddling. He could conceivably be sitting alongside Prescott in the cabinet next month if Labour wins the election and there is a reshuffle.

It is not the first time Prescott’s temper has run amok during the campaign. Last week he told a local reporter, Mark Choueke, to “bugger off” for asking about the defection of a Welsh Assembly member from Labour. Saying he was “a national politician”, he raged: “You’re an amateur, mate. Go get on your bus; go home.”

But Birt is so close to Blair that the Labour leader may find his deputy’s intervention more offensive this time.

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