Police were “reasonable and proportionate” in arresting 12 innocent people after the Westminster terrorist attack, but should review when it’s right to interrogate suspects about their religious views, an official report has said.

The 12 people were arrested after Khalid Masood first mowed down pedestrians on Westminster Bridge, killing four people, before running into the grounds of parliament before he stabbed PC Keith Palmer to death.

The report into the police investigation by Max Hill QC, the independent reviewer of terrorism legislation, concludes that detectives from Scotland Yard’s counter terrorism command got it right and mounted an “impressive” operation.

Police officers, under Operation Classific, hunted for any accomplices to the 22 March 2017 attack, which was the first mass casualty terrorist atrocity to strike Britain in over a decade.

Those arrested were mainly British Muslim, though did include Hungarian and Saudi nationals as well as Masood’s wife.

All were released without charge having come under suspicion for reasons ranging from repeated phone or electronic contact with Masood, connection with an address Masood had lived at in Birmingham and placing money in his bank account for professional reasons.

Hill said questioning people about their religion will cause “understandable concern”, but police believed the attack may have been incited by the violent extremist ideology of Islamic State.



Masood sent a document via WhatsApp and an Apple iMessage justifying violence to a number of people while behind the wheel of the vehicle he used to stage the attack. The document contained passages from the Qu’ran and was called “Retaliation”.

Hill said: “Operation Classific did not lead to the arrest and detention of any person based on ethnicity or religion.

“When challenged by me as to why questions about religious belief and adherence were asked during post-arrest interviews, Operation Classific officers pointed to the religious extremist nature of Masood’s views and intention, evidenced in his final communications before crossing Westminster Bridge on 22 March. The police reasonably believed there was a ‘pro-Islamic State’ element to the attack that day.”

The independent reviewer, a barrister by profession, said police should carry out a review: “It does not follow that it would be appropriate to ask detailed religious questions in every case where a Muslim has been arrested on suspicion of [terrorism].

“I therefore recommend, in the interest of clarity, that the police take this opportunity to review training on the circumstances and extent to which such questions will be necessary in future interviews. I accept, however, that questioning detainees about religion or any other matter occurs with careful thought and planning.”

Hill praised the police operation: “It is against that background that Operation Classific amounted to what in my view was an impressive, flexible, fast-moving investigation which appeared to face significant challenges, but which reached fruition over several days, where a longer exercise might have been understandable or expected.”

The security minister, Ben Wallace, said: “Our comprehensive terrorism legislation gives the police the powers they need to investigate terrorist atrocities and we were all witness to their swift and effective work following the Westminster attack.

“We are pleased that Max Hill QC has concluded that the investigation was impressive, flexible and fast-moving.”

Hill said none of the 12 arrested co-operated with his review.