Thatcher: "Monumental folly"

"It is a piece of monumental folly that puts our security at risk in order to satisfy political vanity," she told the Sun newspaper.

Lady Thatcher's intervention in the political row over the 60,000 strong force came after William Hague committed a future Conservative government to pulling British troops out of the new structure.

Earlier, Mr Blair launched his own offensive on "fundamentally dishonest" media claims that the European defence initiative threatened Nato.

He angrily denied that British forces were joining an EU Army.

"There's no question of British troops being put under the control of any foreign government," he said on a visit to Moscow.

When we are at war, we do it through Nato

Prime minister, Tony Blair

Mr Blair insisted it was right to co-operate with forces from other nations on humanitarian and peacekeeping missions.

"We would contribute in precisely the same way as we do for United Nations missions, Nato missions, Commonwealth missions," he said.

The prime minister added that the force would not be used for conflicts.

"When we are at war, we do it through Nato," he said.