BUDGET airline Ryanair has threatened to sue the government if the heightened airport security measures are not relaxed within seven days.

Security was heightened after police foiled an alleged plot to blow up planes from London to the US last Thursday.

The Irish carrier's chief executive Michael O'Leary said Ryanair was entitled to claim compensation under section 93 of the Transport Act 2000.

"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," he said.

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

He confirmed the threat to sue had been made to the secretary for state transport Douglas Alexander.

"The best way to defeat terrorists and extremists is for ordinary people to continue to live their lives as normal," Mr O' Leary said. "Because of the additional security restrictions imposed by the Government last Thursday, the shambles at the London airports has been anything but normal.

"The UK Government successfully led the return to normality of the London Underground within two days of the 7/7 terrorist attacks."

Ryanair called for the security level at British airports to be restored to normal IATA levels.

This includes restoring the hand luggage allowance for passengers leaving British airports to the normal IATA dimensions of a small wheelie case, which is just 20 per cent larger that 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.

It also called for the passenger body searches to be scaled back from one in two to the normal one in four. "This will reduce the pressure on security staff as well as eliminating the queues and delays at British airports security points."

Ryanair also wanted a reassurance from the transport minister that the next time the government quadruples the number of individual body searches, that they will send in the police and army to help carry out the searches.

"This will at least allow the increased security to be carried out, in an emergency, without the disruptions, delays and cancellations that have characterised the chaos at London airports over the past week," the airline added.