Heathrow airport is likely to be under threat from environmental protests as it prepares to open Terminal 5 next March.
Plane Stupid, a climate change protest group focusing on aviation, refused to deny reports that it infiltrated operation trials in T5 and planned to disrupt its opening.
Airport owner BAA is recruiting 15,000 volunteers to take part in about 100 trials in check-in, security searches and baggage systems. Trials started this month and one planned for next month is expected to involve 2,000 people.
A Plane Stupid spokesman said: “The trials are not difficult to infiltrate. But we could not say what direct action we do or do not plan. Any airport planning expansion is a target and Heathrow is the biggest and most iconic.”
A BAA spokeswoman said there was no evidence that Plane Stupid had infiltrated its trails but BAA carried out criminal records checks on volunteers, she said.