HMS Southampton is one of the ships claimed to be under threat

Portsmouth North MP Sarah McCarthy-Fry was met with cheers during Prime Minister's Questions on Wednesday as she invited support for the dockyard.

But Mr Blair declined to comment on reports that plans have been drawn up to mothball six Royal Navy ships.

The Ministry of Defence (MoD) insists that no decisions have been made.

Labour's Mrs McCarthy-Fry said: "The Royal Navy plays a fundamental role in defending our national security and they should have the resources necessary to meet the vital tasks we ask them to do."

'Country's security'

Mr Blair replied: "I entirely agree with you which is one reason why we have, in terms of investment, in new ships, the largest warship building programme for many years in this country."

And the prime minister said his government was "actually increasing defence spending in real terms year-on-year".

He added: "I also understand, particularly in respect of Portsmouth, that there are 17,000 employed in the naval base there, including 8,800 civilians, and another 26,000 jobs in the wider defence industries in the region.

"It therefore performs a vital task, not merely for Portsmouth, for the region, but for our country's security."