Tesco launches investigation with its engineer contractors following the collapse at superstore site.

British Transport Police have said that the Chiltern railway line will be closed for up to three days following the collapse of a tunnel in Buckinghamshire.

The tunnel was on the site of a new Tesco store being built at Gerrards Cross. The tunnel collapsed yesterday evening shortly after a train driver reported seeing debris falling from the tunnel roof. The Tesco store was in the very early stages of development.

Up to 100 tonnes of rubble fell onto the track along 30m of the 320m-long tunnel. The rubble lay up to 6m deep and was 80m from the South tunnel entrance.

The tunnel was being built by Jackson Civil Engineering, which has a £20m contract to build the concrete tunnel.

Tesco apologised for the disruption caused by the collapse. It said it had launched an urgent investigation with its engineer contractors and was working with the authorities to get rail services back to normal as soon as possible.