The 25-year-old was nabbed following a raid by officers from Scotland Yard's counter-terrorism command (CTC) unit at 7.30am Monday.

The Observer understands that the man, who has not yet been named or charged, is being detained under the Terrorism Act 2000 and questioned on suspicion of commission, preparation or instigation of acts of terrorism.

A second man, aged 20, was arrested at an address in Ilford.

A Met Police spokesman said both men were taken to a central London police station where they are being interviewed by CTC detectives.

He added: "Today's arrests were part of a pre-planned intelligence-led operation into activity, including terrorism overseas. Officers from Met Police were supported by officers from Sussex Police.

"Armed officers were not involved in today's operation."

CTC officers also carried out searches at three residential addresses in Crawley. No details about the raid have yet been released.

Do you know the man? Did you see what happened? Call (01293) 845055 or email matthew.gaw@sussexnewspapers.co.uk