David Cameron usually doesn't do ties, writes political editor Jonathan Walker, but yesterday he made an exception. It wasn't any old tie, you see. It was green - like him.

The young Conservative leader had assembled the nation's media for the launch of the Tory local election campaign, which focuses on the environment.

He's already made cycling de rigueur at Westminster. One day he was pictured riding his bike into the House of Commons, instead of arriving by Jaguar like everyone else, and now every ambitious politician claims to be a cyclist.

It's easy to understand why.

Everybody loves a green. And it seems that this will be the thrust of the Conservative campaign.

Dave arrived on stage, accompanied by flunkies including Local Government Spokesman Caroline Spelman (Con Meriden), and stood in front of a pastel blue backdrop displaying the slogan "Vote Blue Go Green".

It's a phrase designed to appeal to those people who don't actually like Tories much. They're not Tories at all, you see. They're the Green Party in smart suits.

"We have to think global, act local," said Dave. "We have a shared responsibility to act. "

Caroline Spelman remained silent throughout the whole affair, but sometimes nodded enthusiastically. Who could disagree?

What it meant in practice was less easy to fathom. Something about recycling schemes and rubbish collection. Very worthy indeed. But as a rule, aren't we voters more interested in improving local schools and getting council tax bills down than rivers and trees?

Dave, however, has a plan. His aim is to make it OK to vote Tory.

For a good 15 years, it's been difficult for Conservatives to feel proud of their political preferences. They couldn't be sure what sort of reaction they would receive from friends and family if they came out as a Tory. Their's was a love which dare not speak its name.

But if the new Conservative priority is saving the environment, the Tories must be nice people.

Labour's campaign makes a little more sense in this context. Their party political broadcast last night gave us Cameron the Chameleon - a creature who tries to change his colour but is, deep down, an old-fashioned true blue Tory.

Dave dealt with this beau-tifully yesterday. The NHS was in crisis. Didn't the Prime Minister have anything more important to talk about? It was a negative attack, while the Conservatives were being positive, and so on.

Up he climbed, clambering onto the moral high ground and looked down triumphantly at the assembled hacks by his feet. Until one of them asked: "So what sort of creature is Tony Blair?"

Look out, Dave! It's a trap! The smart thing, surely, would have been to refuse to answer.

But it wasn't to be. Blair was a groundhog, Dave declared, and fell back to earth with a bang, joining Labour and the media in the sordid bear-pit of politics.