Volcanic ash: Gordon Brown holds an emergency meeting over flight delays

Ministers said everything was being done to try to help the thousands of Britons stranded abroad by the closure of UK airspace.

But with some clamouring for a relaxation of the restrictions, Transport Secretary Lord Adonis said that following advice from the Met Office it had been concluded that it would "not be safe for flights across most of northern Europe to take place".

Security minister Lord West, a former head of the Royal Navy, said the government was looking at the option of possibly using the Royal Navy to try to bring people home.

Lord West said one of the questions under consideration was which would be the best ports for any operations to happen from. "It will just take a few hours to resolve something, to get something going if necessary," he added.

Ministers also said Prime Minister Gordon Brown was speaking to his Spanish counterpart to see if Britons stranded in North America could be got home via Spain.

Business Secretary Lord Mandelson said Mr Brown had called a meeting of the "Cobra" civil contingencies committee this morning.

Lord Mandelson said: "We will mobilise all possible means to get people home."

The Conservatives last night urged the government to charter ships for Brits stranded in Europe and ensure that border controls did not stop any rescue missions across the Channel.

The Tories also called for the Royal Navy to help bring people home.

Shadow transport secretary Theresa Villiers said it was "hugely worrying" there was no end in sight for the flight ban, as the volcanic ash cloud lingered over northern Europe.

She said ministers should charter ships to bring people home, including troops stranded in Cyprus, and work to ensure that border controls did not prevent a "cross-Channel Dunkirk style" rescue effort by boat owners.

The government should also work with the Civil Aviation Authority, airlines and insurers on producing the data needed for a "full and objective assessment of the risks posed by volcanic ash", the Tories said.

And it should work with the Met Office to ensure a high priority was given to the "accurate assessment of the extent and location of the ash cloud."

Ministers should urge ferry and rail operators to retain their normal pricing structures and not introduce "sudden and excessive price increases."

Ms Villiers said: "With thousands of Britons stuck in airports overseas, it is hugely worrying that there is no end in sight for the flight ban.

"This crisis is costing the economy millions of pounds every day and causing huge amounts of travel misery."