One way or the other, we are going to need HS2, and it is a total disgrace that the Labour Party is now playing politics with the scheme. They are shamelessly courting the sceptic vote – feigning support but unofficially signalling that a Labour government would pull the plug. Ed Balls has said that the case has yet to be made out – even though he went into the last election with HS2 in his manifesto.

Alistair Darling has said it is a “disaster”. Peter Mandelson now claims the whole thing was nothing but an electoral gimmick and should be junked. And you can see why Labour is so tempted, and why they have played this card. They have an economic credibility problem. They are going to have to persuade the electorate that they have some big and unexpected source of funding that will enable them to fulfil all their promises – to cut your fuel bills and plump your pension and subsidise the minimum wage – and the answer is always going to be HS2.

They can also see that the Tories are facing a revolt from those on the route, and from those who aren’t convinced that the scheme represents a good use of public money. Their objective is to make the project politically toxic with a drip, drip, drip of cold water, in a kind of chemical reaction: HS2 + H₂O = H₂SO₄. They hope that continuing anxieties about noise and property prices will cost the Tories votes in key marginals. They are fomenting general hostility to the scheme, and, in particular, they are supporting those who say that investment in HS2 means diverting crucial spending from other parts of the railway network – and there I believe they are talking more nonsense than ever.

This was exactly the case that was made to me, more than five years ago, when the economic crash first happened and we were about to commit to spending £16 billion on Crossrail. It was mad, people said, to build a whole new railway under London when the rest of the Tube network was in urgent need of repair, when we were still using bakelite signalling on the District line and when funds were so desperately short. I remember a passionate denunciation of the scheme from one distinguished transport executive. “Why would you buy a shiny new car and park in front of the house, when the house is falling down?” he asked me.

Well, I think he was wrong then, and I wouldn’t be surprised if he agreed that he looks even more wrong now. We have not only got on with delivering Crossrail – absolutely vital to increase capacity on the London rail network. We have upgraded the Tube as well. We have cut delays by 40 per cent over the last five years, to pick a period entirely at random, and we are going on with a programme of improvements – with new signalling and automation – that will cut delays by a further 30 per cent.

It is now absolutely clear that this decision was right, because the population of London has risen by about half a million in the same period, and is likely to keep rising for the next couple of decades. Without these investments, our public transport system would have rapidly exploded with the strain. Britain has the potential to be the biggest economy in Europe, both in population and output, in our lifetimes; but we simply will not be able to cope, or to give business the platform it needs, if we fail to invest in infrastructure. We need a new supersewer under London, we need a new hub airport, and we need to increase our rail capacity.

There was a time when people like Peter Mandelson and Tony Blair would have recognised this. It is deeply regrettable that the current Labour Party leadership should be so opportunistic and short-sighted as to pussyfoot around about HS2. They are putting short-term tactics before the long-term needs of Britain, and they will not succeed. In 2015 the choice is going to be clear: between fool’s gold, and a Conservative programme for investment and long-term growth.