The two men responsible for the grisly stabbing death of a British army recruiter were being followed by the British domestic security service, MI5, for over eight years before Wednesday's events.

The one confirmed suspect, Michael Olumide Adebolajo, who was filmed admitting to the attacks shortly afterward, had been assessed to be a "peripheral figure" and was not the subject of a large investigation by the MI5 into a possible violent act.

Detectives have yet to question the two attackers (the second one is believed to be Michael Adebowale, 22, but it has not been confirmed), who are still in recovery from gunshot wounds.

Police have also arrested a 29-year-old man and a 29-year-old woman in connection with the attack and charged them with conspiracy to commit murder.

British Prime Minister David Cameron told reporters that "the Independent Police Complaints Commission will be able to review the actions of the police, and the intelligence and security committee will be able to do the same for the wider agencies, but nothing should be done to get in the way of their absolutely vital work."

New footage obtained by Britain's The Mirror show the two attackers being shot by police as they rush the first-responders to the murder scene.

British authorities will now look into when security forces were made aware of the attackers, and how their case was dealt with by MI5.