Police arrest MI5 intruder waving machete

An armed man who stormed the headquarters of MI5 wielding a machete and a large knife was being questioned by police last night.

Two security guards were injured after the man attacked them in Thames House, where both the MI5 Security Service and the Northern Ireland Office are based. Witnesses described the man as white and aged around 40 but it was not believed to have been a terrorist attack.

Police were still investigating the exact sequence of events last night, but it was believed the man first went into the Northern Ireland Office before struggling with security guards. He later gained access to the lobby of MI5, which is responsible for protecting the UK against threats to national security.

A police armed-response unit arrived and the attacker was hit twice with a Taser stun gun before slumping to the ground in the street. His green rucksack and black boots were left on the steps outside as he was taken in an ambulance to hospital where doctors decided he had suffered no ill effects. He was later arrested on suspicion of burglary and assault and taken to Belgravia police station.

The two guards were also treated in hospital where their injuries were not life-threatening and they were described as "stable". Police later said one of the security guards suffered cuts to the hand and the other cuts to his arm.

The incident raised concerns about security measures around Thames House which is on Millbank close to the Houses of Parliament.

The MI5 entrance opens straight on to the street next to the Thames but there are no protective concrete blocks outside and, unlike the headquarters of MI6, the secret intelligence service, at Vauxhall Bridge, there is no perimeter wall.