A lorry containing 8,000 litres of cocoa butter spilled its load on to the M40 in Oxfordshire yesterday, threatening to contaminate the local water system.

The oily liquid spilled out of the lorry tanker following a collision with another HGV at 11.45am and began to seep on to the verge beside the motorway and into the drains.

Firefighters worked with the Environment Agency and Highways Agency to stop the liquid affecting local water supplies.

The crash was near the site of an aquifer - a natural store of underground water - which is used by Thames Water to supply local villages.

Assistant divisional officer David Hanlon, who co-ordinated the fire service's efforts, said: "The split was in the rear section of the tanker, allowing about 8,000 litres of this stuff out. If left, it would have soaked through the chalk and into the aquifer."

The collision between the tanker carrying the cocoa butter and the other lorry took place on the southbound carriageway 300 meteres from the Oxfordshire-Buckinghamshire border near Stokenchurch.

The leak occurred from the rear compartment and the inside lane of the motorway had to be closed.

The driver of the tanker was uninjured. Two people from the other lorry were taken to Wycombe General Hospital, High Wycombe, Bucks, with head and leg injuries.