The difference.

John B explains perfectly what is now the key difference between Labour and the Tories:

I despise almost everything about the Conservative party's policies, leadership and supporters. However, they are actually a political party, rather than a concerted campaign to destroy the British political system and replace it with something weird and Imperial.

That's it, right there: the Tories might do absolutely awful things to the country, but anything they do will ultimately be undoable, because they'll leave our political processes intact.

On the other hand, says Mark Steyn:

If I lived in Britain, I’d vote for Tony Blair’s Labour Party. Yes, yes, I know he’s a nanny-state control-freak and you can hardly pull your pants on in the morning without filling in the form for the Public Trouser Usage Permit and undergoing inspection from the Gusset Regulatory Authority. But on the One Big Thing — the great issue of the age — he’s right, and he’s reliable. And, sad to say, the British Conservative Party aren’t. Their leader, Michael Howard, has been a cheesy opportunist on the war, supporting it at the time, backtracking later, his constantly evolving position twisting itself into a knot of contortions even John Kerry might find over-nuanced. Most other Tory heavyweights — ex-Thatcher cabinet ministers like Lord Hurd and Sir Malcolm Rifkind — are more straightforward: They’re agin the war. They’d have no time for his frightful American clothes or his ghastly hamburger diet, but, social distaste aside, they’re Michael Moore Conservatives.

And that's true, too. Blair might destroy our constitution and turn the UK into a police state, but domestic politics is unimportant in comparison to the current big picture. Free the world first, then free ourselves. And we absolutely do not want anyone in charge right now who might even consider using the phrase "acceptable level of violence".

However, there's one key reason that I wouldn't risk voting Labour: the Labour Party have deluded themselves into believing that they can win elections without Blair. They really think that the electorate are voting for the party, not its leader. If they win, we'll see a leadership challenge — probably not a successful one, but it won't be the last. Yes, Blair is right and reliable on the one great issue of the age, but a vote for Labour is no longer a vote for Blair — not long term.

The Conservatives, on the other hand, will remain just as useless a shower of amoral authoritarian bastards no matter who's in charge. That's kind of reassuring.