ALISTAIR DARLING, the Transport Secretary, has been remarkably consistent in the past four years in the promises he has made on road tolls. He insists that they are the only alternative to concreting over the countryside with more roads, but always ends by saying that tolls are “a decade away”.

In 2002, when Mr Darling took up his post, a decade meant that tolls could have been clearing roads of congestion in time for the London Olympics in 2012. Now, the Department for Transport talks of 2015 as being the earliest date for charging by the mile for all roads.

It is hard to find a transport expert who does not fervently believe that tolls are the solution to rising congestion. There is less consensus on technology, but Germany has already introduced a charging system that involves tracking lorries by satellite.

A Ministry of Transport report concluded that the technology for charging by the mile “would probably take about a year or 18 months from the time the Government gives the necessary encouragement”. That was in 1964.

Mr Darling has referred repeatedly to the need for consensus if tolls are to be introduced. What he fears is the vociferous minority of drivers who commute on the busiest roads and would pay far more — up to £1.34 a mile — under a national toll system. Until recently the Tories were cautiously supportive, but now they seem to be swinging back to the road-building agenda.

Look out next year for another ministerial endorsement of tolls, coming your way in 2017.