I have two problems with High Speed 2, the project to build a super-fast rail link between Euston and Birmingham given approval by the government on Tuesday. The first is that £17 billion could surely be spent on transport (or other) projects far more useful than conveying business executives between the capital and the second city half an hour faster than at present. The second is that if business executives travelling between Birmingham and London really, really must reach their destinations half an hour sooner than they do now, why don't they just get an earlier train?

If that means their waking up at 6.30 instead of 7.00 in the morning, I'm sure the tax payer could meet the cost of the high performance alarm clocks required, should the nation's economy depend on it. But where do the capital's 2012 mayoral contenders stand on the issue of HS2?

A spokesperson for the incumbent Boris Johnson (Conservative, as you may have heard) responded to the government's green light by saying that "the Mayor has always believed there was a case for investing in a high speed rail network," and was pleased that the government had "listened to the points he has made regarding its impact on the quality of life for thousands of residents in the capital."

According to Hillingdon Conservatives, Boris has been meeting members of the local residents' group Ruislip Against HS2 this very day. Last July, he apparently annoyed the then transport secretary Philip Hammond by arguing that its impact on Londoners had not been given enough consideration and that Euston should be structurally adjusted to accommodate the extra passengers.

Ken Livingstone (Labour, as you may also have heard) too has been to Hillingdon and addressed residents' concerns about the HS2 route. He was there last May, shortly after a previous visit by Boris to a borough that swung so heartily behind him in 2008. In that same month Ken laid out proposals for lessening the impact on people in Camden and before that he told Ealing it shouldn't pass through that borough at all. But there's no question that he favours HS2 going ahead. Indeed, he's said he favours the service stretching all the way to Waterloo as well.

Brian Paddick (Liberal Democrat, as at least some of you will have heard) couldn't be reached for comment today but we can be sure he shares the line of London's Lib Dems in being "supportive of the development of high speed rail infrastructure in the UK," and believing it will help the country's economy by "opening up opportunities and creating easier access to London for regional business." They add: "There needs to be a real effort to look at the impact the project will have on Euston station and the homes around it.'

No fundamental difference, then, between Boris, Ken and Brian. It's been left to the Green Party's Jenny Jones to break with the consensus. She tells me she's "totally against HS2" and in complete agreement with her party's response to the government's, ah, green light for the project.

This calls the decision "a mistake" based on flawed assumptions about job creation and a unproven business case. It argues that IT solutions should be promoted to reduce transport demand and says that high speed rail "is not a 'get out of jail free' card for carbon emissions and climate change." Jenny adds that "there's been no thinking" about the necessary Euston upgrade, let alone providing the money it would take. She had nothing to say about government grants for high-powered alarm clocks, but give her time.

That's a second big tick from me for Green thinking on transport and the environment, the first being for the report they commissioned on a possible Londonwide pay-as-you-go road-pricing system. And two big ticks go quite a long way to becoming a cross on a ballot paper.