Dear Tony Blair

To the Labour leader. Think about Terry Major-Ball, Candace Gingrich and Roger Clinton, and be warned: never mind the hard left, it's potentially embarrassing relatives that could threaten your future ...

You had better own up now. Best to get it out in the open, in the Robert Hughes style, before the tabloids get a sniff of the story. The likely cause of your eventual political downfall is becoming increasingly obvious. Not the Tory party, nor even the hard left in your own party which hopes to inflict defeat on you over your plans to reform Clause IV. No, the real threat to your political future lies closer to hand: it's your relatives.

The evidence is overwhelming: when politicians rise to the pinnacle of power, their relatives start crawling out of the woodwork to embarrass them. Newt Gingrich was the latest to suffer this week, when Candace, his gay half-sister, turned up in Washington to attack his conservative views on homosexuality. Bill Clinton has had his work cut out to cope with his real brother, let alone the people who claim to be his brother. No sooner had Ronald Reagan got to the White House than his daughter started campaigning against him. Jimmy Carter's main relief at losing the presidency to Reagan was that it meant his brother, Billy - the one with the peanuts - could no longer embarrass him.

Things would be fine if the trend were confined to the United States. But the signs are that it is spreading to Europe: Silvio Berlusconi's government collapsed after his brother was arrested in a fraud inquiry. But, as with most political trends started in the US - monetarism in the Eighties, communitarianism in the Nineties - Britain is proving receptive. Take John Major as an example. First he had to put up with his brother, Terry Major-Ball, becoming a cult figure. Now his son is embarrassing him with rumours of romance at work at Marks & Spencer. And Mrs Thatcher's big weak spot may yet turn out to be her devotion to her son, Mark.

So, Tony, the evidence is virtually inescapable: if you get to Number 10 you are almost certain to be embarrassed by a relative within the first few months of your administration. In the past, Labour prime ministers would face a sterling crisis; now it's more likely to be an uncle or a brother crisis.

You will just be getting used to the official dinners and the trips abroad, the free tickets to the Cup Final and the surging sense of power, and some long lost cousin will start expounding outrageously right-wing free- market views, denouncing your socialism. Your support for the traditional family is well known: has Peter Mandelson made sure the tabloids will not drag up a far-flung Blair who is a several-times-divorced single parent on housing benefit?

But the US examples suggest your kids might generate greatest embarrassment: make sure Ewan does not run off with his Man United posters, your passport and your credit cards, heading for Kota Kinabalu.