The post-terror attack lockdown around Westminster began to lift as London authorities opened Westminster Bridge and Westminster Tube Station on Thursday (23 March) afternoon.

A Transport for London (TfL) spokesperson confirmed the move to IBTimes UK as MPs returned to work at the historic Houses of Parliament.

Prime Minister Theresa May told the House of Commons that eight people have been arrested at six addresses in Birmingham and London as part of the police's investigation.

The Conservative premier also paid tribute to PC Keith Palmer, 48, who was fatally stabbed by the British-born assailant on Wednesday.

"He was a husband and a father, killed doing a job he loved. He was every inch a hero," she said. "And his actions will never be forgotten. I know the whole House will join me in sending our deepest condolences to his family – and to the families and friends of all those who have been killed or injured in yesterday's awful attacks."

Foreign Office minister Tobias Ellwood, whose brother was killed in the 2002 Bali bombings, was also praised for delivering CPR to Palmer.

"We will remember the extraordinary efforts to save the life of PC Keith Palmer, including those by my Rt Hon Friend the Member for Bournemouth East," May said.

"And we will remember the exceptional bravery of our police, security and emergency services who once again ran towards the danger even as they encouraged others to move the other way."

London terror attack: Met police hold minute's silence for fallen officer ITN

The death count from the attack has been revised to four, with at least 29 injured – seven critically. The self-styled Islamic State (Isis) have claimed responsibility for the attack through its al-Amaq news agency. May said the attacker was known to MI5, the domestic intelligence service.

The Queen has said her "thoughts, prayers and deepest sympathies" with all those affected by yesterday's attack.

"Following yesterday's shocking events in Westminster, Prince Philip and I are sorry that we will not be able to open the new Scotland Yard building as planned today, for very understandable reasons," the monarch said. "I look forward to visiting at a later date.

"My thoughts, prayers and deepest sympathies are with those who have been affected by yesterday's awful events.

"I know I speak for everyone in expressing my enduring thanks and admiration for the members of the Metropolitan police service and all who work so selflessly to help and protect others."

Westminster attack
Union flags fly at half-mast in front of Elizabeth Tower (Big Ben) at the Houses of Parliament, London Niklas Halle'n/AFP