A teenager has reportedly been arrested in connection with the Parsons Green tube bombing yesterday.
Scotland Yard say that an 18-year-old was arrested by Kent Police in the port area of Dover, with Metropolitan Police Deputy Assistant Commissioner Neil Basu claiming the apprehension is 'significant'.
"Although we are pleased with the progress made, this investigation continues and the threat level remains at critical," he said.
Police confirmed that the explosion on the London Underground on Friday morning was a terrorist incident.
Armed police and emergency services were called to Parsons Green tube station after an explosion in one of the train's carriages.
In a statement, the Metropolitan Police said: "Officers from the Met's Counter Terrorism Command are investigating after an incident on a London tube train this morning.
"Police were called at approximately 08:20 BST on Friday, 15 September to Parsons Green Underground Station following reports of a fire on the train.
"Deputy Assistant Commissioner Neil Basu, the senior national coordinator for CT policing, has declared it a terrorist incident.
"Officers from the Metropolitan Police Service and British Transport Police attended the scene, along with colleagues from the London Fire Brigade and London Ambulance Service."
The statement continued: "At present we are aware of a number of people who have suffered injuries. It is too early to confirm the cause of the fire, which will be subject to the investigation that is now underway by the Met's Counter Terrorism Command.
"The station remains cordoned off and we are advising people to avoid the area."
Eyewitness Robyn Frost told the BBC: "I was just about to walk into the station and there was two people standing outside and a woman sitting on the pavement with blood around her and she was crying, she was really hysterical.
"I walked into the station there was blood on the floor and people screaming 'get out'."
The suspected device is reported to have been hidden inside a bucket, which itself was concealed inside a large supermarket cool bag.
Major General Chip Chapman told Sky News: "This doesn't look like a high-end from ISIS such as TATP or if it was it failed significantly or the booster or detonator so at the moment you have to keep an open mind.
"That said, of course, the most devastating land-based terror attack in Europe, in Madrid, has a similar modus operandi, so the MO could suggest something.
"But is could just be something as benign as chemicals of someone going to work with some flash, but we can say that at the moment it's not a high-explosive than functioned because the blast and shockwave would have killed multiple people."
Featured Image Credit: PA