The cost of decommissioning and cleaning up Britain's Sellafield nuclear site have been revised upwards to �53 billion ($81 billion, 73 billion euros), the National Audit Office said.

The cost has gone up by �5 billion and work at the site on the northwest English coast is taking much longer than planned, the NAO said in a report.

The Nuclear Decommissioning Authority, which owns Sellafield, aims to clear the site by 2120.

Sellafield is Britain's "largest and most hazardous nuclear site", the report says.

Nuclear operations began in the 1940s and Britain's worst ever nuclear accident happened at the site in 1957. Sellafield stopped generating electricity in 2003.

It is now a reprocessing and waste storage facility which deals with spent nuclear fuel from Britain and other countries.

Britain's nuclear reactors provide about 20 percent of the country's energy needs and the government is placing nuclear power at the heart of its low-carbon energy policy.

The EU in September recommended approval of Britain's ambitious plan to build its first nuclear plant in a generation -- the Hinkley Point project -- with backing from French and Chinese energy giants, after ruling that it met state aid rules.