14 pints-a-day-Hague

And, according to author John Rentoul, young Tony was such a handful at Edinburgh's Fettes College - a school sometimes known as "Eton in a kilt" - that he came within an ace of being expelled.

He was constantly flouting the rules and was once beaten for his bad behaviour.

Weekend hippie

"He was more than happy to push the public school's rules to breaking point and a little beyond, but he - mostly - stopped short at the stage where his defiance would inflict serious damage to either his person or his academic career," the book states.

The book also delves into the prime minister's time as a "weekend hippie" living virtually hand-to-mouth in London, promoting rock groups.

There is little doubt that the latest revelations will add more colour to the prime minister's background.

But the need for political leaders to appear "interesting" is a recent phenomenon and has seen the inevitable comparisons drawn between Mr Blair, Tory leader William Hague and, to some extent, Liberal Democrat boss Charles Kennedy.

Until his extravagant 14-pints a day boast, William Hague was mostly remembered as the precocious, political-anorak and Thatcherite who addressed the party conference in his teens.

The trainspotter image was always far from the full truth about the Tory leader, but it stuck and his advisors were eager to replace it with a racier style.

Part of this saw him telling trendy men's magazine GQ about his teenage drinking habits while working as a delivery boy for his father's company, Hague's Soft Drinks.

"Anyone who thinks I used to spend my holidays reading political tracts should have come with me for a week," he said.

"There were crates of soft drinks and barrels of John Smith's bitter, and we delivered them mainly around the working men's clubs.

"We used to have a pint at every stop - well the driver's mate did, not the driver - and we used to have about 10 stops in a day. "

'Billy Fizz'

Suddenly the boy William started looking more like a lager lout than a political geek - and there were fears the claim might even have gone too far.

Known as 'taxi Kennedy'

And, like Tony Blair's stowaway story, it was soon thrown into doubt by locals who claimed he had always been known as Billy the Pop or Billy Fizz.

Only Charles Kennedy has, so far, not been troubled by claims that he has tried to beef-up his image. And there is probably a good reason for that.

When he was first elected to parliament in 1983 he was only 23 - the youngest MP at the time - and was seen as an earnest, political animal.

But, more importantly, he already had a reputation as a bit of a bon viveur who enjoyed a drink or two, or even three or four, and who liked his food.

'Bit of a lad'

According to a University friend he was known as "taxi Kennedy" for his habit of refusing to walk anywhere if he could avoid it.

And, despite his obvious interest in politics, he was hugely unsure about what he wanted to do in life - first thinking of teaching or journalism.

So, in many ways, Mr Kennedy already had the "bit of a lad" image before he became his party's leader.

And with typical irony it saw some wondering whether he was too lightweight for the job.

The lesson from all this, perhaps, is that youngsters currently harbouring ambitions of becoming a party leader had better start working on their bad boy images now - just don't go over the top.