Former Soviet leader Mikhail Gorbachev has warned of the dangers of leaving intact tonnes of chemical weapons dating from the Cold War.

Stockpiles of nerve gas, skin blistering agents and chemical warheads are widely feared to be vulnerable to theft or to leakage.

Our project is aimed at eliminating the environmental consequences of the Cold War and the arms race

Mikhail Gorbachev

At a news conference in Westminster Mr Gorbachev urged political leaders from across the world to address the problem.

He called for billions of dollars to tackle Russia stockpiles which are estimated to exceed 40,000 tonnes.

As well as chemical weapons Mr Gorbachev warned that there were 200 obsolete submarines which needed their nuclear reactors decommissioning - but the full scale of the task was still not known.

Arms race

"Our project is aimed at eliminating the environmental consequences of the Cold War and the arms race.

"It is a terrible legacy we are trying to deal with."

He added: "We are still learning. We will have to know exactly how many tanks with chemical weapons or chemical agents were buried underwater in the seas and the oceans.

"There are more than 200 submarines that are out of commission that still contain nuclear reactors that have to be disposed of."

Mr Gorbachev said that the Soviet Union and the US each spent the equivalent of $10,000bn on the arms race.

"Now tens of billions, perhaps hundreds of billions, of dollars will be needed to destroy these weapons."

The former Soviet leader was appearing in his capacity as president of the Green Cross - an organisation concerned with the clean-up of chemical and biological weapons.

11 September

He said he had noticed a greater sense of urgency in the wake of the 11 September terror attacks.

Dumped submarines are just one problem

He acknowledged the desire of the US to defend itself but warned of the dangers of new arms races.

"I think we should understand that the government of the US, the president of the US, are responsible for the security of the nation - we understand that.

"But at the same time, as the friends and allies, partners, of the US, should be in a position to say to them that while doing that, don't re-launch a new arms race.

"We are still dealing with the consequences of the old arms race, without starting a new one."

Mr Gorbachev was having lunch at the Foreign Office before holding talks with Conservative leader Iain Duncan Smith.