LONDON (AP) — British police scoured a huge London park on Friday for an ex-soldier who escaped from prison while awaiting trial on terrorism charges.

The Metropolitan Police confirmed the search of Richmond Park in the city’s southwest, which involved two helicopters and officers on the ground, was connected to the hunt for Daniel Abed Khalife. The 21-year-old slipped out of Wandsworth Prison on Wednesday morning while working in the kitchen, apparently by clinging to the underside of a food-delivery truck, police said.

Khalife is accused of planting fake bombs at a military base and of violating Britain’s Official Secrets Act by gathering information “that could be useful to an enemy.”

He was discharged from the British army after his arrest earlier this year and had denied the allegations. His trial is set for November.

His escape has prompted extra security checks at airports and the Port of Dover, the main boat crossing from England to France. But activity focused on Richmond Park, 2,500 acres (1,000 hectares) of woods and grassland about 5 miles (8 kilometers) from Wandsworth Prison.

Opposition politicians demanded to know how Khalife managed to escape from the medium-security prison and why he was not being held at a maximum-security facility. The Conservative government has said there will be an independent investigation.

Metropolitan Police counterterrorism commander Dominic Murphy said there had been no confirmed sightings of Khalife since his escape and described the prisoner as “very resourceful.”

“He was a trained soldier – so ultimately he has skills that perhaps some sections of the public don’t have,” Murphy.