Officers swooped after reports that the men were taking delivery of propane gas canisters at an industrial unit in Blackburn.

The men, believed to be in their 30s and 40s, were held under the Terrorism Act 2000 amid fears they were connected to the recent bomb plots in Glasgow and London.

However, detectives have now ruled out any links to terrorism as they believe the premises were being used to cultivate cannabis.

Lancashire Constabulary defended the arrests under terror legislation as "necessary under the circumstances". It said it recognised it was a "very sensitive time" for all communities but urged the public to continue to report any suspicious activity.

The operation was launched on Tuesday after a member of the public became concerned about the two men seen on the Furthergate Industrial Estate in Birley Street.

Eyewitnesses said a delivery driver arrived at a unit on the estate with about five canisters and that two Asian men appeared shortly afterwards. An unmarked police Ford Focus carrying two officers immediately pulled up and the men were arrested on suspicion of terrorism offences.

A second consignment of around five canisters arrived at the premises close to the town centre shortly afterwards.

A Lancashire Constabulary spokesman said: "Following a search of the industrial premises on Birley Street in Blackburn, police can now confirm that the premises would appear to have been used to cultivate cannabis. More detailed searches of the premises are planned.

"The two men in custody are now being held on suspicion of offences under the Drugs Act, and are not being dealt with under terrorism legislation."