By Jon Silverman
BBC Legal affairs analyst
Ryanair cancelled dozens of flights at the height of the security alert
Ryanair's threatened lawsuit over the cost of implementing the new security measures raises a potentially fascinating legal issue.
The government issued its emergency directive under powers granted to the Transport Secretary under the 1982 Aviation Security Act.
The legislation permits the Secretary of State to serve directions on airports and airlines; to require modifications to airports; to serve enforcement notices; and to inspect airports and airlines.
More than any other form of transport, aviation practice is global and Britain's 1982 act consolidated two decades of international agreement contained in the Chicago, Tokyo, Hague and Montreal Conventions.
An annex to the Chicago Convention specifically requires member states of the International Civil Aviation Organisation to establish national security programmes to meet the needs of international air traffic in their country.
Government lawyers would no doubt argue that this obligation was being carried out when the latest guidance on baggage restrictions, prohibited items and searching was issued.
However, Ryanair is basing its case on the 2000 Transport Act.
Section 93 of that act repeals the 1982 Aviation Security Act in the event of "severe international tension, great national emergency or actual or imminent hostilities."
Ryanair boss Michael O'Leary wants compensation
The 2000 act makes it an offence to contravene or fail to comply with a government directive.
But it also provides for compensation to be paid by the Secretary of State for "direct injury or loss arising from compliance with a direction."
Until now, this section has not been tested but in-house legal teams at Ryanair, easyJet and British Airways are now studying it with some care.
They are looking to see if it can be used as leverage either to get compensation or, at least, to persuade the government to scale down some of the emergency measures.
The airline industry has long been notoriously litigious but it seems there is no precedent for a compensation claim resulting from the impact of tightened security.
If a case came to court, the issue of proportionality would probably be central. Are the restrictions imposed by the government through the British Airports Authority proportionate to the threat?
The airlines are hoping to provoke a wider debate about government help in offsetting the cost of increased security
But aviation experts believe that, rather than incur further losses with an expensive lawsuit, the airlines are hoping to provoke a wider debate about government help in offsetting the cost of increased security.
Traditionally, such costs have been borne solely by the industry but within the European Union, as a whole, there is a growing view that it is time national governments bore their share of the burden.