Hague has nothing to lose

But within minutes of the statement Mr Campbell was briefing some journalists that he hadn't meant it and there was no way the prime minister would agree to such a kamikaze project.

He apparently claimed he had simply fallen victim to the temptation to give story-hungry hacks something to write about, and had immediately regretted it.

But the idea grew wings and was splashed all over the following day's newspapers.

Ever since then, Downing Street has been rowing back and spokesmen have come up with any number of reasons why such a debate is not sensible. And the reasons are all legitimate.

Sweaty and unprepared

It is certainly the case that, unlike the US, the two contenders confront each other regularly at question time.

But what really worries all sitting prime ministers is that, by conceding to such a debate, they are handing the political agenda over to the leader of the opposition, who has nothing to lose.

Richard Nixon learned that lesson when he agreed to the first ever TV debate with Kennedy - and threw away his chances of election by appearing unshaven, sweaty and unprepared.

Politicians are more sophisticated than that nowadays - but they have learned the lesson that you don't offer your opponent any platform.

Prime ministers also like to use their status during election campaigns to give themselves added clout.

Ducking out

The minute they agree to a face-to-face debate with their opponents they are accepting they should be treated as equals.

That not only gives the official opposition a boost, but it offers minority parties such as the Liberal Democrats - who would have to be included in any TV debate - the sort of platform they could otherwise only dream of.

Kennedy might call the tune

In other words there is absolutely no mileage for the prime minister in agreeing to a TV debate.

Any negative publicity he gets from ducking out of a confrontation can be easily brushed aside with excuses about Britain being different to the US.

And it was becoming increasingly clear that Downing Street had to stamp on this one before it became a significant election issue.

William Hague will have a few days' fun taunting the prime minister for being "chicken" but, by election time, the issue will have been forgotten.