Phase one works for the £50m project will prepare the ground for the installation of new infrastructure and additional track between Oxford and Worcester - due to be laid throughout 2010.

Engineers will reposition nearly 10 miles of existing track to make room for the new line. Since the Oxford, Worcester and Wolverhampton line was singled in the late 1960s the track follows a route that consists of sections of the old southbound or northbound lines. In many places these existing tracks have been centred, leaving insufficient space for a second line to be laid. Therefore, existing track has to be repositioned to provide the space required for a double-track railway.

Work will also involve constructing 21 miles of new surface concrete cable route, installing 30 miles of new cable and relocating 60 sets of signal equipment. In addition, engineers will lay extra track through the 157 year old Chipping Camden/Mickleton tunnel, designed by Brunel, using a high-tech construction train. The work in the tunnel will include removal of the existing track, ballast and drainage system. More than 12,000 tonnes of materials will be removed from the 811m long tunnel. A new 2,000m drain will be installed to alleviate flooding in the future.

The initial programme of work will take place over a six week period from 18 July to 1 September while the design of the core engineering work is being carried out. Trains will be diverted or replaced with bus services while the line is closed.

Chris Rayner, route director for Network Rail, said: "One of the biggest challenges for this first phase is finding the opportunity to carry out the work without disrupting the daily operation of the railway and the community. To minimise any disruptions, we will be constructing infrastructure off-site whenever possible, providing a diversionary route as an alternative and carrying out our work in phases without having to close a long stretch of line at one time."

Train operator First Great Western's project manager for the scheme, Martin Barnett, added: "The North Cotswolds line is a particularly congested part of the railway, which means small delays tend to have more of an effect on our customers than they should. Once complete in early 2011, the redoubling of the track will provide extra capacity for more trains to carry more customers should demand continue to increase, and help sustain improved performance in the area."

As part of its ongoing effort to reduce the impact of railway operation on the environment, Network Rail will be cleaning most of the existing ballast and recycling it after removing all the contaminants.