The row over who said what to whom at a gathering in Corfu this summer is not only about politics, power and money, it is also about manners.

George Osborne broke a social rule every bit as important as Gordon Brown’s economic rules – he leaked details of private parties and confidential conversations for political advantage.

That these conversations took place on a yacht owned by a publicity-shy Russian billionaire and at the holiday villa of a wealthy member of a banking dynasty only compounded the error. That Lord Mandelson was the victim of the briefings made it more likely that the tables would be turned.

It is the breach of etiquette, rather than any potential breach of parliamentary rules, that seems to have most irritated Nathaniel Rothschild, Mr Osborne’s old friend from Oxford and host in Corfu. “It ill behoves all political parties to try and make capital at the expense of another in such circumstances,” he wrote in his letter to The Times yesterday. “Perhaps in future it would be better if all involved accepted the age-old adage that private parties are just that.”

The rich and powerful have a code of silence every bit as powerful as the Mafia’s omertà. The assumption is that those who join the Family will obey the rules because they, too, might one day have something – either personal or professional – that they would prefer to keep private.

It is particularly important that this code is adhered to when senior figures from different political parties are mingling socially in a way that would never have happened in a more ideological age. Mr Rothschild is not the only well-connected power broker to bridge the political divide. At Elisabeth Murdoch’s 40th birthday party recently, David Cameron and Mr Osborne brushed shoulders with David Miliband, Tessa Jowell and Tony Blair. These influential, politically androgenous hosts have to be able to guarantee that what guests say will go no farther. Their own reputations, as well as those of their guests, depend on it.

Mr Rothschild is convinced that Mr Osborne, a fellow member of the Bullingdon Club in their student days, broke the code when he returned from Corfu by spreading rumours about the Business Secretary’s dealings with Russia’s richest man and letting it be known that Lord Mandelson had “dripped poison” about the Prime Minister into his ear. The result was the political equivalent of a horse’s head to the Shadow Chancellor’s bed. “Nat hopes they can still be friends,” one ally of Mr Rothschild said. “But he thinks George has shown very bad manners.”

As the son of a baronet and a debutante, Mr Osborne might have been expected to understand better the etiquette of being a house guest. But he is also one of the Tories’ sharpest political operators. He could not, it appears, resist embarrassing Labour's own strategic capo di capi when he returned to the political front line. He did not realise how dangerous it would be.

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