Westminster terror victim Pc Keith Palmer's family want answers over alleged failures in Parliament's security system, an inquest has heard.

Khalid Masood, 52, stabbed the officer to death after fatally striking four people as he ploughed through pedestrians on Westminster Bridge in a rented car.

The Old Bailey has heard fixed posts for armed officers at Carriage Gates, where Pc Palmer, 48, was on duty, had been replaced with roving patrols.

Two authorised firearms officers (AFOs) on duty on March 22 have said they had never seen instructions issued in 2015, which said they should focus on the gates when they were open.

Pc Lee Ashby and Pc Nicholas Sanders said they believed they were required to patrol a wider area in New Palace Yard.

Dominic Adamson, representing Pc Palmer's widow Michelle, said on Wednesday: "We can conclude confidently that the system that was in place when it shifted from a fixed post to a mobile patrol left officers at the gates materially more vulnerable as a result of that change?"

Pc Sanders said: "Along with all of the other places of threat in that sector as well sir, yes."

The inquest has heard no AFOs had been near the gates for almost an hour before the attack, and the experienced firearms officer was asked what he would have done had he been in that position.

He said he would have gone to the sound of an "explosion" as Masood crashed his car into a railing.

Susannah Stevens, representing Pc Palmer's family, said she was asking the questions because no firearms expert has been called to give evidence at the inquest.

"All the family want is to have an opportunity to put questions to see whether or not the failures in the system would have made a difference," she added.

The inquests continue into the deaths of Pc Palmer, Kurt Cochran, 54, Leslie Rhodes, 75, Aysha Frade, 44, and Andreea Cristea, 31.