At No 10, the strategy is to insert a thin-bladed stiletto, almost imperceptibly, into the new Tory leader. At No 11, the Brownites would prefer to bring a huge, blunt, double-handed broadsword down on his head.

The difference of approach was evident during Cameron’s debut at Prime Minister’s Questions. Blair was accommodating, feigning to be flattered and faintly puzzled that Cameron should seek to join him on the political centre ground. Brown was more direct: “Money!” he bawled repeatedly, demanding that the Tories put their money where Cameron’s mouth is.

The Brownites are eager to attack Cameron on class and past. Every strand of the Chancellor’s DNA instructs him to rub the Tory leader’s nose in his own privilege, by pigeon-holing him firmly in Eton, Oxford, Whites Club and Notting Hill. The frontal assault would have the double benefit of allowing the Brown camp to portray their man as astringent, hard-nosed and uncompromising, as distinct from Cameron and Blair (emollient, smiling, saccharine).

Blairites, however, believe that an attack along class lines could be counterproductive. Blair (Fettes and Oxford) has never felt comfortable on that sort of ground, and ad hominem politics has never been his style. Moreover, there is a danger that by raising issues of class and privilege, Brown runs the risk of appearing a political dinosaur. This is, of course, precisely how Cameron’s advisers intend to portray him: a booming, doomed Goliath towering over a tactically superior David, or rather “Dave”.

Blair, however, prefers more nuanced tactics: appearing to welcome the newcomer, while questioning his motives, and insisting that the Tory leopard can never truly change its spots.

A memo to party members from Ian McCartney, Blair’s minister without portfolio, gave a flavour of the Blairite approach: “The Conservatives’ current rebranding exercise is simply putting a new gloss on the same old Tory politics . . . we need to show what these ‘modern Tories’ really stand for.”

Alastair Campbell gave notice of how seriously Labour takes the Cameron threat when he wrote, in these pages, that the new man “will be a good target”. In a move that Machiavelli would have applauded, Campbell portrayed Cameron as a replica of what voters most dislike about new Labour: himself. “We are both basically spin-doctors.”

This will be the main thrust of the Blairite attack, to portray Cameron as a shallow sound-bite, a PR professional with a right-wing past.

“He was Norman Lamont’s spin-doctor,” wrote Campbell, spinning for all he is worth. “He was a PR man for a TV company, and you can’t get more spin-doctory than that.” Unless, of course, you are Alastair Campbell.

Whether the party takes the direct Brownite approach or the more subtle Blairite stance (or a combination of both) Labour believes there are serious chinks in Cameron’s armour, and will exploit them ruthlessly. His youth will be portrayed as inexperience, his verbal fluency as facile spin, his charm as smarm, his first from Oxford the mark of a man too smart for his own good.

Shaun Wooodward, who preceded Cameron as Tory MP for Witney before defecting to Labour, has been detailed to investigate potential weaknesses in Cameron’s style, presentation and policies. His views on the flat-rate tax and his pledge to pull his MEPs out of the European People’s Party grouping in the European Parliament will be painted as evidence of hardline right-wing leanings.

In the double-think characteristic of the spinner’s art, Cameron will be made to look inexperienced as an MP, but experienced in the ways of old Toryism, having worked with Lamont, Major and Howard.

While the attack dogs may steer clear of a direct attack on the basis of class, they are likely to bring up his privileged past in other ways, most notably by clubbing Cameron with his club memberships. Cameron has made much of bringing more women into the Tory party, yet he belongs to Whites club, which does not admit any women as members.

Potentially more damaging, and certainly more amusing, is his membership of the Bullingdon Club at Oxford. Exclusive, expensive and famously destructive, the Bullingdon was memorably satirised by Evelyn Waugh as the hard-drinking “Bollinger Club” (in the novel the members memorably stone a fox to death with champagne bottles). Tom Driberg said of a Bullingdon meeting: “Such a profusion of glass I never saw until the height of the Blitz.” There are no eyewitness accounts of Cameron attending the Bullingdon Club — yet.

Already Lord Gould, Blair’s pollster, has been asked to carry out focus group surveys to establish the impact of the “Cameron effect” during his first few weeks of leadership.

According to the polling group Populus, surveys already show the broad terrain on which Labour will have to take him on. Cameron does disproportionately well among ABs, voters that historically form the bedrock of the Tory vote when the party is winning and among whom the Conservative decline has been most marked. He also does better among younger voters and has made inroads into the persistent Conservative Party brand negatives.

Polls towards the end of the leadership campaign indicated that he was regarded as significantly more likely than David Davis “to get the Conservatives in touch with ordinary people”. Once Cameron’s honeymoon is over, the Labour machine will begin to counter-attack in earnest. Yet many of the weapons at their disposal may rebound on them: emphasising Camerons’s youth may make this Government seem old and stale; tackling him over class and privilege smacks of old Labour resentment; accusing him of spin-doctoring invites the response: physician, heal thyself.

The knives are out in Downing Street, but some of them are double-edged swords.

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