The Government survived a major Labour backbench revolt last night to secure the backing of the House of Commons for its plan to replace Britain's Trident nuclear deterrent.

The Government won the main motion by 409 votes to 161 - a majority of 248. Earlier, an amendment tabled by rebel Labour MPs to delay Trident renewal was defeated.

The rebels claimed more than 90 Labour MPs voted for delay, with others abstaining, making it the biggest revolt since the Iraq War.

One of the Labour rebels, Oxford East MP Andrew Smith, said he had "always loathed" nuclear weapons.

He said the estimated £20bn cost of the project would be better spent tackling climate change, improving schools and hospitals and ensuring conventional troops were better equipped.

With David Cameron's Tories voting for Trident replacement, the Government was never in danger of defeat.

However, the scale of the rebellion is another blow for the authority of Tony Blair as his premiership enters its final months.

Earlier in the day, two more ministerial aides - Stephen Pound, the parliamentary private secretary (PPS) to Labour Party chairman Hazel Blears, and Chris Ruane, the PPS to Northern Ireland Secretary Peter Hain - resigned in protest.

Mr Blair defended the decision to retain Trident and said it was essential a decision to begin work on the design of a new submarine fleet was taken now.

"I think that is essential for our security in an uncertain world," he told MPs at Prime Minister's Questions.

"We can't put this decision off. We have to take it now."

In an olive branch to opponents, Mr Blair said future Parliaments would be able to revisit the issue as the orders for the submarines would be placed in the next decade.

Witney MP Mr Cameron also emphasised his party's support for maintaining Trident.

"Replacing Britain's independent nuclear deterrent is in the national interest," he said.

"In a dangerous and uncertain world, unilateral nuclear disarmament has never been and will never be the right answer."

Evan Harris, Liberal Democrat MP for Oxford West, said a premature decision to renew Trident would be "wholly counter-productive" to the major global effort required to prevent nuclear proliferation and the possession of nuclear weapons by states like Iran.