A teenager has been arrested on suspicion of terrorism following Friday’s attack on a London Tube train.

The attack on a morning commuter train left dozens injured, and today officers arrested an 18-year-old man at the Port of Dover.

He was arrested under section 41 of the Terrorism Act and is being held at a police station in Kent.

The Metropolitan Police’s senior national co-ordinator for counter terrorism, Deputy Assistant Commissioner Neil Basu, said: “We have made a significant arrest in our investigation this morning.

“Although we are pleased with the progress made, this investigation continues and the threat level remains at critical.

“The public should remain vigilant as our staff, officers and partners continue to work through this complex investigation. We are not, at this time, changing our protective security measures and the steps taken to free up extra armed officers remain in place.

“This arrest will lead to more activity from our officers. For strong investigative reasons we will not give any more details on the man we arrested at this stage.”

The Met has reported that the man was arrested at the Port of Dover, and a spokesman for the Port authority said staff were supporting both the Met and Kent Police with the investigation.

Chief Supt Nicola Faulconbridge from Kent Police said: "There is nothing to suggest there is a specific threat to Kent at this time and our thoughts remain with all those affected by the events in Parsons Green.

"All calls to Kent Police are assessed, as is usual, based on threat, harm, risk and vulnerability and will continue to be resourced and responded to on this basis."

Kent Police is liaising with the Home Office to regularly assess the national threat levels and what that means for the county.

Chief Supt Faulconbridge continued: "There are additional patrols, both armed and unarmed, across Kent which will remain for as long as we believe is necessary. Members of the public are urged to carry on their normal business and routines but we ask them to remain vigilant.

"These events are rare in Kent. Should anyone ever find themselves in an incident like this our advice is to run to a place of safety, hide and then call us on 999 when it is safe to do so."

The town's MP, Charlie Elphicke, has tweeted that he has spoken to Kent police an thanked officers for their 'outstanding work'.

Last night it was confirmed the country's terror threat level had been raised to critical - meaning another attack is expected imminently.