THE IMPOSITION of the highest ’critical’ terrorist threat warning at UK airports in the early hours of August 10 caused massive disruption.

London Heathrow - one of the world’s busiest airports that handles the most international flights - suffered the worst cancellations and delays as security staff initially struggled to cope with instructions to stop passengers carrying onto the plane almost anything other than the clothes they stood up in, and particularly any liquids that might be explosive. Restrictions were gradually relaxed, but disruption at many UK airports continued for several days.

There was substantial diversion of short haul passengers to rail. In the first five days Eurostar carried 40000 extra passengers through the Channel Tunnel using spare capacity on existing services, although no extra trains were operated. However, GNER did run 10 extra trains between London and Edinburgh up to August 14, on top of a timetable that sees two departures an hour for most of the day. These relief trains carried 3000 passengers, with thousands more packing into the scheduled services.

Virgin Trains looked at beefing up its less-frequent service from London to Glasgow, but decided that its Pendolino fleet was already fully stretched. With a half-hourly London - Manchester service available since 2004, Virgin accepted valid air tickets on the first day of the crisis without any means of recovering payment from the airlines. Perhaps the chance to show off its new tilting trains to potential customers was reward enough.

It is too soon to judge whether the sheer scale of what appears to have been a plot to blow up as many as 10 planes over the Atlantic will bring any lasting benefit to inter-city rail operators. And terrorists have also attacked railways, most recently in the suburbs of Mumbai on July 11 where explosions on seven commuter trains killed 207 people and injured more than 700.

A UIC study tour is taking security experts to Asia this month to examine ways of protecting public transport users. That this is an international issue was underlined by other recent alerts, ranging from two suitcases containing propane left in a train approaching Dortmund and a luggage locker in Koblenz last month to the discovery of a plot to blow up the PATH metro tunnels under the Hudson River between New York and New Jersey.

However, there is one important difference between plane and train. Quite a small device will cause a plane to crash, killing everybody on board. Most bombs on trains don’t even derail them, although passengers in the coach affected may be killed or injured. Even under the most severe conditions of a London Underground tube tunnel less than 4m in diameter, only 21 out of several hundred passengers died in the suicide bomb attack on the Piccadilly Line on July 7 2005.