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The battle for London Mayor has moved 250 miles north to Gateshead, where Tory contender Boris Johnson has been sticking his rhetorical boot into the Labour incumbent.

Johnson won laughs and applause from party activists at the Conservative Spring Conference as he eased his political stiletto between Ken Livingstone’s ribs.

He was merely repaying the compliment after Labour dedicated an afternoon to bashing Boris at their spring conference in Birmingham two weeks ago.

But while Labour Minister Hazel Blears called Johnson a “nasty, right-wing elitist, with odious views and criminal friends”, Boris opted for a more subtle approach.

“I know I am facing one of the wiliest and most redoubtable opponents in British politics … a man equipped as if by millennia of evolution with a prehensile tail with which to cling to office,” he told his appreciative audience.

“He has said some wise things. For instance, he said that only a ghastly dehumanised moron would get rid of the Routemaster bus, a point he then proved by getting rid of them himself.

“Just as the dinosaurs finally ceded dominion of the earth after their interminable epoch, so it is dawning on us that Ken Livingstone is visibly being transformed into “Ken Leaving-Soon” and the great Newtosaurus Rex has finally had its day.”

The mutual exchange of invective shows how the political temperature is rising ahead of the May 1 election, with the two contenders neck and neck in the polls.

The contest is already being seen as a proxy for the next general election - due by 2010 but potentially coming as soon as summer next year.

Johnson says it would be “momentous” if Labour loses the London Mayoral race.

You can see Johnson telling me why he is standing for Mayor here, and explaining why Boring Boris and Old Boris are two sides of the same coin here.