Ryanair today issued the Government with a seven-day ultimatum to relax airport security measures or risk being sued for compensation.

The request for a return to usual security measures was made by the Irish no-frills airline to Douglas Alexander, the Transport Secretary.

Security at airports was heightened last week after an alleged bomb plot was uncovered to blow up passenger jets bound from Britain to the United States using explosives smuggled aboard in hand luggage.

Ryanair said that if security was restored to "normal" International Air Transport Association (IATA) levels within the next seven days then the airline would "not make any claim for compensation which it is entitled to under the provision of section 93 of the Transport Act 2000".

But the Department of Transport shrugged off the threat, saying that it had no intention of changing security levels in the next week.

"The security regime in place at UK airports is necessary because of the level of security threat and is kept under constant review," said a spokesman. "We have no intention of compromising security levels nor do we anticipate changing our requirements in the next seven days."

The argument between Ryanair and the Government unfolded as the Association of Chief Police Officers revealed that officers from every police force in the UK had been drafted in to help with the investigation into the alleged plot, described by Scotland Yard as of a similar scale to the September 11 attacks.

Airlines remained jittery too: a British passenger aircraft made an emergency landing in southern Italy today after a holidaymaker found a bomb threat scribbled on a sickbag in her seat pocket.

The Boeing 767 jet, operated by Excel, a charter airline, was carrying 269 passengers from Gatwick to Hurghada in Egypt when the captain requested permission to land in Brindisi, according to Italian air traffic controllers. Police searched the aircraft and said the threat was a false alarm.

Michael O’Leary, the Ryanair chief executive, issued his ultimatum this morning saying that the Britain people had to respond to terrorism by living their lives normally.

"The shambles at the London airports has been anything but normal," he said.

"The UK Government successfully led the return to normality of the London Underground within two days of the July 7 terrorist attacks. It is important that they now restore security at the London airports to normality and remove some of these nonsensical, and (from a security perspective) totally ineffective restrictions which were introduced last week.

"If they don’t, and if they allow these restrictions to stay in place, then the Government will have handed the extremists an enormous PR victory."

Among its demands, Ryanair said the hand luggage allowance for passengers leaving British airports should return to the normal IATA dimensions of a small, wheeled case, which is just 20 per cent larger than the current restriction of a "large briefcase" dimension.

"There is no difference in security whatsoever between a large briefcase and a small carry-on wheelie bag", the airline said.

The airline also wants passenger body searches scaled back from the current one in two to the previous one in four, which still allows any suspect passengers to be individually body-searched.

Ryanair also announced today that in order to "get Britain flying again" it was releasing one million seats for sale on more than 100 routes, priced at £25 one way including all taxes and charges.

Paul Charles, director of corporate communications at Virgin Atlantic Airways, said today that Virgin was in discussion with airport operator BAA about possible compensation.

Mr Charles went on: "We are not seeking compensation from the Government, but we think the Government should pay for extra security at airports.

"The threat is against the UK, and in the same way that the Government pays British Transport Police to patrol the railways, the Government should pay for airport security."

The British Airline Pilots Association (Balpa) also joined in the row over the security regime, complaining that the emergency measures had prevented pilots from taking necessities such as contact lens solution into their cockpits and risked bringing Britain's airports to a standstill.

"If we don’t learn from the lessons of the past two weeks we shall be in trouble and aviation could grind to a halt for all the wrong reasons," said the chairman of Balpa, Captain Mervyn Granshaw.

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