Parsons Green District Line London
Armed policemen stand by cordon outside Parsons Green tube station Kevin Coombs/Reuters

British special forces have been given 'shoot to kill' instructions following the recent terror attack in London, according to some reports.

This comes after several people were injured on an underground train when an explosive device went off near Parsons Green station.

The Daily Star reported that some members of the SAS and the Special Reconnaissance Regiment will be travelling on the underground and around parts of London in disguise.

A source told the Daily Star: 'The task force is comprised of some of the most experienced special forces personnel in the Army.

'The unit is composed of some of both male and female personnel from the Special Reconnaissance Regiment who are trained killers and can pose as couples while travelling on public transport.'

The UK terror threat level was temporarily increased to the highest possible mark – 'critical' – but this was subsequently dropped back down to 'severe', meaning that a an attack is no longer imminent but is still highly likely.

Police are still questioning two men, an 18-year-old and a 21-year-old, on suspicion of terror offences.

Police are searching two addresses in Surrey in connection with the arrests – one in Sunbury-on-Thames and another in Stanwell.

A third property in Hounslow has also been searched as part of the investigation, Scotland Yard said.

Islamic State (Isis) has claimed responsibility for the attack, but while speaking to the Andrew Marr Show on Sunday (17 September), Home Secretary Amber Rudd said there was "no evidence" to suggest so-called Islamic State was behind the attack.