A freedom of information request has revealed enough details about High Speed Two, the Government's proposed high-speed rail line to Scotland, to make a trainspotter's eyes go moist with anticipation. The trains are going to be double-decked and carry 545 people from a station near Wormwood Scrubs to Glasgow in 2 hours 42 minutes. We also know that Booz Allen Hamilton, the consultants employed by the Department for Transport to produce a study, have costed it at £29 billion, with an optional £10 billion add-on to Leeds and York, to be raised through a mixture of private and public finance.

What is rather more vague is how the railway will pay its operating costs. One thing is for sure, they are not going to be met by the passengers. If anyone can find a new railway line anywhere in the world that makes a genuine profit, I would love to know about it. And don't bother writing in to point out that Eurotunnel has finally moved into profit, 15 years and numerous financial restructurings after the Channel Tunnel was opened. It is the car and lorry shuttle that makes the money, not Eurostar, which still loses £100 million a year.

It goes without saying that the taxpayer will be picking up the tab. Even with the most expensive rail tickets in Europe, passengers are currently only meeting half the £10 billion annual cost of running Britain's railways - and that is a system whose mostly 19th-century infrastructure has already been paid for. Even if the new trains could do London to Glasgow in 15 minutes, the chances of selling enough tickets at a high enough price to repay the cost of £29 billion of new infrastructure are zero.

There are some who cannot stand the concept of taxpayers subsidising rail passengers, full stop. There exists a pressure group that for at least 20 years has been campaigning for rail lines to be concreted over and made available for lower-cost coach services. But you don't have to be in favour of extinction of the railways to be concerned at the direction in which rail travel is going. There is a perfectly respectable case, on social and environmental grounds, for subsidising railways. It is just that current government spending on rail travel is poorly targeted to meet either social or environmental objectives - and if we are not careful the billions to be spent on a new high-speed line will be even less likely to achieve them.

Using taxpayers' money to subsidise the railway system can only ever be justified if it is in order to provide a genuine public service. Yet increasingly, trains are becoming social inclusion-free zones, the poor driven off to make room for the rich.

An open return from London to Manchester now costs £247: fine if you are a business traveller and your company will pay the fare. True, if you are a leisure traveller who can book your ticket a few weeks in advance, you might just secure one of a handful of seats teasingly sold off for a tenner. But if you are a taxpayer on a modest salary who needs to travel at short notice, say for a job interview or because a relative has been taken ill, the railways no longer offer a practical means of travel. You are paying your taxes to help the wealthy travel in style - while you are stuck on the motorway in a cheap coach.

It is hard to see how a new £29 billion high-speed line is going to rectify this injustice. More likely, services will be franchised to a rail operator that will shamelessly target the upper end of the market - not least northern and Scottish MPs travelling to and from their constituencies at 100 per cent public expense.

While the Government looks into this prestige project, less glamorous public transport services continue to be starved of cash. As Transport Secretary in 2005, Alistair Darling axed proposed tram lines in Leeds, Liverpool and several other provincial cities. He cited a National Audit Office report that criticised some earlier schemes in

Birmingham, Sheffield and Manchester for failing to make an operating profit in their first year - hardly surprising given that the lines were deliberately built through depopulated wastelands in order to spark regeneration.

If we are going to subsidise rail travel at all, every penny spent must be subjected to a public benefit test. The subsidised service must be open to everyone who might possibly want to use it. It must remove many hundreds of cars from the road, easing congestion and cutting significant amounts of pollution, or provide a nucleus that leads to the regeneration of a rundown part of a city. For a multibillion-pound inter-city service to provide some vague benefit such as reinvigorating national pride or reducing carbon emissions by a few wisps by replacing a couple of scheduled airline services a day is not enough.

To put it another way, if this proposed £29 billion high-speed rail line is not going to be open to an unemployed Glaswegian electrician travelling to London in search of a job, forget it. Our taxes would be better spent reducing the fares on our existing rattling old train services to ensure that we all get something for our money.

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