One traditional justification for subsidising railways is to divert traffic from the environmentally damaging modes of travel by air and road. But it is not clear that high-speed trains, as distinct from conventional trains, are more environmentally friendly than air. Moreover, by releasing airport slots now used for short routes such as London-Paris or Paris- Brussels for longer air journeys, the introduction of high-speed trains actually increases air travel.
Very little car travels consists of journeys between the centres of large cities, which are the natural market for high-speed trains. It is certainly desirable to reverse the trend towards longer car journeys, but subsidies to the competition are an expensive and ineffective way of doing so. The problem is best tackled by lower and better enforced speed limits, perhaps accompanied by increases in the cost of motoring.
We need better rural and regional passenger services and more rail freight. We do not need high-speed trains.