British pilots have termed as 'dangerous' and 'flawed' the government's decision to place armed sky marshals on passenger jets flying across the Atlantic, following heightened concern about terrorist attacks.

The British Air Line Pilots' Association (BALPA) was seeking an urgent meeting with Secretary of State for Transport Alistair Darling to discuss the policy, which they described as 'dangerous' and 'flawed'.

The association, which said it doesn't want 'guns on planes', has advised pilots to refuse to fly if they do not feel happy carrying armed marshals posing as passengers.

Darling said he would meet the pilots to discuss their 'misgivings' and said they would be told when an undercover marshal was on a flight.

He defended the government's decision to allow plainclothes officers with low-velocity weapons on selected flights. He said it was a responsible and prudent step that would be used where appropriate.

Darling said their use was only one of a number of measures and a last line of defence, together with increased screening of bags, to deter terrorists. But he warned that passengers could face longer queues at airports because of the heightened state of security.

"Most of our efforts are rightly focussed on the screening of passengers' baggage. The best thing is to try to stop people getting on the aeroplane in the first place", he said.