Andrew Harding: "Russia's decaying nuclear submarines have been causing increasing concern"

He promised £3m to clean up the world's worst dumping ground for nuclear reactors.

Mr Cook visited Murmansk in the north of the country where he examined the environmental and safety concerns.

Some experts believe a nuclear explosion could occur in the region the at any time.

The former Soviet submarines are in a poor state

An explosion would affect large areas of Russia and northern Europe with nuclear fallout.

"I don't want to be alarmist but of course this is a serious area of concern here," Mr Cook said.

He said British aid would be targeted at providing storage for nuclear waste such as converted World War II barge storing warped and broken nuclear fuel rods in the region.

It has been described as a "floating Chernobyl".

Other nuclear blackspots in the region include a bay where 21,000 nuclear fuel rods are lying on a beach entirely exposed to the elements.

Andrew Harding: "Mr Cook described the environmental hazards in Murmansk as a real concern to the rest of the world"

Some environmental groups fear that nuclear waste has simply been dumped at sea.

But Russian authorities are playing down the problem.

Vladimir Volko, of the Atomflot nuclear plant, said: "I think it is not necessary to worry about the situation with the nuclear material.