Airlines banned hand luggage on flights out of the United Kingdom on Thursday and warned of massive delays after British police said they had disrupted a plot to blow up aircraft in mid-flight.

All carriers, including British Airways, United Airlines and Virgin Atlantic, stepped up security on news of the plot to smuggle bombs on board a flight between Britain and the United States.

Passengers were banned from carrying any hand luggage on board flights, including mobile phones and handbags, airlines and airport authorities said.

All liquids were banned on board except for essential medicines. Milk for babies would be allowed on board but must be tasted by the accompanying passenger, UK airport operator BAA said in a statement.

"British Airways, acting on instruction from the UK Government, wishes to advise passengers that no items of hand baggage can be carried on board any aircraft departing any UK airport," the airline said in a statement.

"The UK government has advised that this instruction will apply to all airlines operating from UK airports."

The Department of Transport said in a statement on its web site that security at all UK airports had been increased and additional security measures had been put in place on all flights.

BAA, which operates three of London's biggest airports including Heathrow, said all passengers would be hand searched and their footwear and all items they carry would be X-rayed.

It added that all passengers on flights to the United States would be subject to a secondary search at the boarding gate.

"We are cooperating fully with the authorities," said a spokesman for United Airlines, which is one of just two US airlines, along with American, that have landing rights at London's Heathrow Airport.

Carriers not flying on transatlantic routes were also affected. Low-cost airlines Ryanair and easyJet said significant delays should be expected.