Britain remains on the highest terror threat level with armed police patrolling major events across the country after the arrest of the teenager suspected of the London train bombing as he tried to flee the country.

The 18-year old was detained on suspicion of being a terrorist by Kent Police in Dover yesterday morning in a development hailed as “significant” by detectives. Armed police also evacuated and searched a house in Sunbury, Surrey, in connection with the Tube train attack at Parsons Green which left thirty people injured.

Yesterday, armed police and sniffer dogs were at Premiership football matches, a horse racing event and a food festival in England. Metropolitan Police Commissioner Cressida Dick joined her frontline staff on some of London’s busiest streets and travelled on the tube as she highlighted an increased police presence.

Meanwhile, Scottish police said they will be reviewing all “significant events” taking place over the coming days and will increase security where appropriate but Assistant Chief Constable Bernard Higgins stressed “there is no intelligence to suggest there is any specific threat to Scotland”.

He said: “The public should expect to see armed officers on foot patrol at key locations and crowded places across the country. Please do not be alarmed by the presence of these armed officers. These measures are being taken to increase security at these sites, and to reassure residents, businesses, workers and visitors so they can go about their daily lives as normally as possible.

“Along with event organisers, we will also be reviewing all significant events taking place over the next few days and will increase the security footprint around those events where it is deemed appropriate.”

The device which exploded at Parsons Green reportedly contained the explosive triacetone triperoxide known as TATP or the Mother of Satan, as well as nails, but is thought to have only partially detonated from inside a shopping bag and bucket. The country's top counter-terrorism officer indicated that a potential network of plotters could have been involved.

Assistant Commissioner for Specialist Operations of the Metropolitan Police Service Mark Rowley said police were “chasing down suspects”, while suggestions were made by Donald Trump that the bomber was known to Scotland Yard.

The suspect was captured in the port area of Dover, which is the busiest ferry hub in Europe and serves as a commercial gateway to the French coast, including Calais and Dunkirk.

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.”

A key strand of the investigation has focused on CCTV as officers comb through footage. Police said they have spoken to 45 witnesses and 77 images and videos have been sent to detectives by the public.

Security minister Ben Wallace suggested CCTV images of the bomber could be released as part of the manhunt for those responsible, but Scotland Yard subsequently denied there were any plans to do so.

The Scottish Government Resilience Room has been activated following the London attack and First Minister Nicola Sturgeon and key cabinet colleagues are said to have been fully briefed in connection with the increased threat level.

Holyrood officials have confirmed that extra security arrangements will be in place at the Scottish Parliament while the heightened threat level exists.