A leak of highly radioactive nuclear fuel has forced the closure of Sellafield's Thorp reprocessing plant.

The leak was enough to half fill an Olympic-size swimming pool and contained about 20 tonnes of uranium and plutonium fuel.

The mixture leaked through a fractured pipe into a huge stainless steel chamber which is so radioactive that it is impossible to enter.

Income from the Thorp plant, calculated to be more than £1m a day, is supposed to pay for the cleanup of redundant nuclear facilities.

Meanwhile a leaked government document has claimed environment secretary Margaret Beckett is blocking plans to build new nuclear power stations.

The prime minister has personally endorsed "keeping the nuclear option open" and is planning a government statement on a change of policy before the summer.