The five men arrested near RAF Fairford may have been conducting a ‘dry run’ for a future attack, a source has warned.

The British nationals were detained on suspicion of explosives offences and terrorism on Sunday after three vans were found near RAF Fairford in Gloucestershire.

The air base has been used by the US military to carry out strikes against Iran.

Residents evacuated from about 85 households were able to return home on Monday, but a cordon remained in place around the vehicles as counter terrorism officers continue to examine the scene.

Today, the head of Counter Terrorism Policing said that no improvised explosive devices were found in the three vans discovered near RAF Fairford, but a quantity of petrol was recovered.

Fears remain as the investigation continues.

Security expert Will Geddes told : ‘This seems to have been a dry run rehearsal before an attack.

‘Many terrorists get picked up during what we call hostile surveillance detection – when they’re taking photographs, driving routes, etc. I think this was their penultimate dry run before actually doing the attack itself.’

‘Other governmental facilities are on high alert right now. Confidential sources have told me that they are very anxious at the moment about possible follow-up attacks. This situation is not over or contained,’ Geddes told .

‘The farmer who saw the team run into the woods mentioned another 3 or 5 individuals actually running off who weren’t detained. It’s possible that only half of those involved have been detained.

‘The others, through desperation and fear of capture, might accelerate their plan to one of the other targets they may have considered.’

One former counter-terrorism officer told the Telegraph that detectives will be looking into whether the alleged plot was a ‘dry run’ before an actual attack.

He said: ‘One possibility is that this was a hostile reconnaissance operation and they were carrying out a dry run before the actual operation.

‘That might explain why the police do not appear to have found anything such as explosives in the vehicles.

‘The barrels that were removed look like they might have been empty, so police will want to know whether they were checking out the lay of the land. If so, then these chance arrests were very fortunate indeed.’

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