It was about 2.40pm and a division bell was ringing, calling MPs to vote on a pensions bill, when shots were heard in the grounds of the Palace of Westminster, one of the most heavily guarded buildings in the world.

Minutes earlier a black car had driven into pedestrians on a footpath on Westminster Bridge, before crashing into a railing outside parliament.

Conservative MP for Watford Richard Harrington had just finished addressing the chamber on a new pensions bill when he was told the vote was being suspended.

SEE ALSO: Watford MP Richard Harrington was finishing speech on pensions bill when shots were fired in Westminster

"I had just voted and was waiting for others to come and do the same when we were told we were being locked in the chamber until further notice," Harrington told the Observer.

"We all know the risks we take when we come into office, but you just can't believe it when it actually happens."

Eight arrests have been made following the attack yesterday that left four dead and seven in a critical condition.

Those that died are PC Keith Palmer (below), Aysha Frade who worked at a London college, a man in his 50s and the attacker.

Watford Observer:

Mr Harrington said: "PC Palmer was part of a small team that always protected parliament.

"I got to know him after stopping to chat on my way into work.

"It was obviously the last thing you expect when you say hello in the morning. It is terribly sad.

"He directly gave his life to protect others - and his actions should be commended."

Conservative MP and Minister for Counter-Terrorism, Tobias Ellwood, who used to represent Hertfordshire, was also hailed a hero after he performed CPR on PC Palmer.

SEE ALSO: Former Herts MP hailed a hero after trying to save life of police officer stabbed to death

Describing "sombre" scenes inside parliament, Mr Harrington said Michael Gove had witnessed the attack on his way into the chamber - where 400 MPs were gathered.

A vote was underway in the main debating chamber on a pensions bill when the deputy speaker announced “there had been a serious incident and we were not going anywhere".

Well-rehearsed security procedures were immediately put into place as the doors to Parliament were locked and MPs, staffers and visitors were ordered to remain where they were.

SEE ALSO: Herts Police response is 'strong visible presence'​

Some were locked in corridors and others in public halls and offices as heavily-armed police began combing the historic, rambling buildings.

About 1,000 people including MPs were taken to the nearby Westminster Abbey and held there for several hours.

Watford Observer:

Watford MP Richard Harrington was inside parliament when the attack took place

Others were held inside Westminster Hall, where they stayed until 8pm.

Mr Harrington said: "I walked to Victoria when I was released and I have never seen London like it. It was eery. It was bitterly sad."

Mr Harrington said he wouldn't stop having schools visit him in parliament, and he already takes precautions when he holds surgeries.

He added that police in Watford were remaining vigilant.

Prime Minister Theresa May, who was only a short distance from the scene of the attack, was immediately rushed into a silver Jaguar and driven at high speeds away from parliament.

She went to 10 Downing Street before leaving for an unknown destination for around an hour, returning to deliver a statement outside the official residence.

Speaking on Thursday, she said the attacker was British-born and known to the police and intelligence services.

She joined other defiant MPs who stood side by side in silence this morning as they came together to remember those injured and killed in the attack.