When it comes to managing the public finances, one would think that avoiding making commitments to spend £32 billion on a capital project with dubious and unproven economic and social benefits would rank quite highly in the current climate. Unfortunately, you'd be wrong, for this is exactly what the coalition government is trying to do with HS2, its high speed rail plan to link London with the North.

£32 billion. That's the equivalent of £1,200 for every household in Britain. Or £51 million for every constituency. In this Parliament alone, the government will spend £800 million on consultants, enough to pay the salaries of 19,000 police officers.

All this will make for an exciting debate on Thursday when the project comes before the House of Commons for the first time. And with neither the debt crisis nor Downing Street's aversion to supply-side economics showing any sign of abatement, it will be tempting to many to think that cracks may be appearing in the coalition's resolve and that another u-turn could be in the offing.

HS2 certainly bears similarities to other u-turns of the recent past in that where grassroots opposition has grown up in the absence of a proper national debate. HS2's consultation was dangerously amateurish, with vast swathes of information - such as the proposed route north from Birmingham to Leeds and Manchester and beyond - kept from the public. The New Economics Foundation described the DfT's consideration of alternative measures to HS2 as poor.

Like other coalition u-turns, the ability of HS2 to harm those that it seeks to help is also in evidence. Take the North-south divide. One big argument that proponents use is that it will address regional imbalances in our economy. But seven out of ten jobs - according to the DfT's own numbers - that are created will actually be in London and the Southeast. The experience of other countries even suggests that once a high speed rail line has been put in, more companies will re-locate to the capital.

Again, the likelihood that HS2 will deliver benefits to our economy is highly uncertain, something that was acknowledged by the DfT itself as recently as 2007. In its Eddington Transport Study, the department said: "Because the UK is already well connected, the key economic challenge is therefore to improve the performance of the existing network...large projects with speculative benefits and relying on untested technology, are unlikely to generate attractive returns."

And then there is the much-touted environmental premium that HS2 will deliver, giving the country a low-carbon infrastructure for a low-carbon age. Except that it probably won't. Or, to quote an IET & Royal Academy of Engineering Consultation submission from July "We cannot see any justification

for the claim that HS2 as proposed will reduce emissions."

The last argument for HS2 that needs demolishing is the issue of capacity. Known by its supporters as the 'killer argument', the basic premise is that West Coast Main Line is about to run out of capacity unless a new line is built. Except it's bunkum. Capacity constraints as they are can easily be rectified by expanding the number of standard class coaches on the existing line, with relatively modest modifications to the infrastructure. HS2, on the other hand, won't be able to deliver any benefit for at least 15 years between London and Birmingham and a further seven for Leeds and Manchester. Even then, its impact will be questionable, as current DfT calculations are based on HS2 being able to run 18 trains per hour, something that has never been done on a high speed railway before.

All of which makes it clear that, for the coalition, HS2 remains a political project rather than a transport one. But even so, their lack of judgement seems surprising. Far from the patronising tag of nimby that gets applied to anyone who disagrees with them, our supporters transcend all political, income and regional divides, from the Taxpayers Alliance and Adam Smith Institute to the Green Party and the New Economic Foundation. We are also passionately pro-rail, as our manifesto demonstrates. Let's hope the government sees sense before it is too late.

Follow Jerry Marshall on Twitter: www.twitter.com/hs2aa