Environmental activists are planning to disrupt hundreds of flights by blockading key areas in Heathrow’s giant new terminal when it opens in the spring, The Times has learnt.

Supporters of Plane Stupid, an antiaviation group that caused chaos by occupying a taxiway at East Midlands airport last year, have infiltrated passenger trials taking place over the next three months at Terminal 5.

BAA, Heathrow’s owner, is introducing special measures to protect the terminal but admits that it has no way of knowing whether volunteers in its trials are linked with Plane Stupid.

Now it has emerged that both the aviation industry and the environmental group spied on each other in an attempt to gain intelligence on rival plans and tactics. People working for FlyingMatters, a lobby group funded by BAA, have contacted Plane Stupid posing as environmentalists interested in supporting their action. Meanwhile, activists working for Plane Stupid have tried to glean information about the activities of FlyingMatters by ringing its offices and pretending to be journalists.

BAA is recruiting 15,000 volunteers to take part in 100 trials of the £4.3 billion terminal’s check-in, security search and baggage systems. The trials began this month and the biggest, due to take place in December, will involve 2,000 volunteers.

When it opens in March, Terminal 5 will be able to cope with 35 million passengers a year, enabling Heathrow to handle many more flights than the 480,000 take-offs and landings that are at present allowed by the Government. BAA hopes that that limit will be increased once Terminal 5 is fully operational.

Plane Stupid, which organised the “climate camp” that blockaded BAA’s offices at Heathrow in August, has a link on its website to the Heathrow owner’s volunteer registration page. A member of the group said: “We have managed to get hundreds of our supporters registered as volunteers and they will be checking out the terminal because we consider it to be the number one target for direct action.”

He said that the group was considering protests, including a demonstration during or soon after the opening of the terminal. “Terminal 5 is an icon representing the breakneck expansion of air travel in this country and the aviation industry’s failure to address the damage it does to the climate.

“Our supporters are ordinary people and BAA will have no way of knowing whether its volunteers are just plane geeks or activists committed to taking direct action.”

In August BAA obtained an injunction banning leading members of Plane Stupid from taking part in protests at Heathrow. But Plane Stupid has been careful not to identify its supporters and takes care to ensure that only a small number of people know details of its plans for direct action. It managed to keep the location of the Heathrow climate camp secret until it opened, despite a huge police operation at the airport.

A BAA spokesman said: “This pressure group would do far better to engage with the aviation industry in proper debate on climate issues rather than in publicity stunts.”

Michelle Di Leo, director of FlyingMatters, said: “Again Plane Stupid are indulging in irresponsible gestures.

Their actions impact most on those they profess to be protecting: families who holiday once a year, ethnic minorities who rely on air transport to visit family, and farmers in the developing world reliant on UK consumers.”

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