Costain has started work on a £200m project to build Britain’s biggest road-rail freight interchange on a 200 ha site near the junction of the M4 and M25.

The London International Freight Exchange project includes £50m of rail infrastructure that will be built on and off site – such as a spur to the Great Western main line – soil cleaning and 250 000 m2 of warehousing.

Steve Tillman, project manager for developer Argent, said Costain sold the land to Argent last year on the understanding that the contractor would be used on the project. Argent has now given the go-ahead for preliminary works at the site in Colnbrook, Berkshire.

Tillman said he was confident that a public inquiry to be held next year would approve the project, as it was in keeping with the government’s ideas for an integrated transport policy.

He said: “London International Freight Exchange takes 50 million heavy goods vehicle hours off the road each year. That fits in with the government’s white paper on transport.”

Tillman said the inquiry should last 12 to 16 weeks and that he expects a result in six to 12 months. This means that Costain will not start in earnest until 2001. But he said the first train would run 18 months after planning approval was received.

The site is classified as greenfield even though it is a series of waste-filled gravel pits. Opponents of the scheme say that it would generate more than 2500 local deliveries annually, despite its beneficial effects.

The Colnbrook scheme has a catchment area of 8.5 million people - about 15% of the UK population.

This compares with existing schemes in Daventry, Northamptonshire, which has a catchment area of 6% of the UK population and Hams Hall, which has an 11% catchment area.

The scheme is the largest of a new breed of transport interchanges intended to relieve road traffic congestion.