Lax security faulted in deadly attack near UK parliament

An investigation into the first of a string of terror attacks to hit Britain in 2017 faulted lax security for one of five deaths near the Houses of Parliament. (AFP/NIKLAS HALLE'N)

Khalid Masood, a 52-year-old British convert to Islam with no proven allegiance to a foreign terror group, drove a car at pedestrians on Westminster Bridge over the River Thames on March 22 last year.

He killed four people before stabbing police constable Keith Palmer to death with two knives outside the Houses of Parliament.

The attack injured around 50 and ended when police shot Masood dead.

A coroner's inquest - an official fact-finding hearing that can be the basis for further legal proceedings - found that the police constable's death could have been averted had better security been in place.

"Due to shortcomings in the security system at New Palace Yard, including the supervision of those engaged in such duties, the armed officers were not aware of a requirement to remain in close proximity to the gates," the coroner said.

"Had they been stationed there it is possible that they may have been able to prevent PC Palmer suffering fatal injuries."

London counterterrorism police chief Neil Basu, accepting the findings, said his force was "deeply sorry".

Security measures had since been reassessed and beefed up, he added.

"However, everything that we can possibly do to improve the position further - and we will await the chief coroner's detailed conclusions - will be done," Basu said.

The probe drew on the testimony of witnesses and survivors of the attack.

Palmer's widow Michelle told reporters that "the police haven't been very open about their investigation" into what had gone wrong.

"How could Keith have been left alone, unarmed, guarding an open gate at one of the most iconic buildings in the world and one of the country's top terrorist targets?" she asked.

"He was left at a vulnerable location with no protection to die."

The gates of the Houses of Parliament in the heart of London were being protected by unarmed officers at the time.

The coroner said the police constable tried to challenge Masood as he came charging at the gate.

Masood stabbed Palmer to death in what the corner described as a "ferocious" attack.

Britain endured a tumultuous period following the Mar 22 rampage. It witnessed four further terror attacks - including three in London.