Calm and stoic mood on Westminster streets
The roads around the Houses of Parliament are choked with traffic and tourists at the best of times but on Wednesday there is an extra buzz about the place for Prime Minister's Questions at midday.
It is the best day to see your MP, as they are nearly all in the building. Queues to get into Parliament start forming early in the morning. The protests in Parliament Square seem noisier and more colourful than normal.
Things start to wind down after the main event but there is still a festive atmosphere in nearby pubs, as people from all parts of the UK - down in London for the day to lobby their MPs - swap stories and buy drinks.
Now the wide roads leading in all directions to the Houses of Parliament are silent and empty, blocked off by police tape, following a deadly terror attack. The police cordon covers an area of a few square miles and keeps being extended.
"You are now in the de facto press pen," shouts a police officer as we are moved back further down a side road behind a more distant line of tape. "I have to make this road sterile."
The incessant clattering of helicopters overhead and the occasional police siren have replaced the roar of traffic.
Foreign TV crews mill about at the police cordons, their mobile phones clamped to their ears as they explain to their editors why they can't get near the scene.
A few locals chat to the reporters. The mood is calm and almost resigned.
"It was a matter of time I suppose," says one man. "I'm old enough to remember the IRA days. I remember them saying 'we only have to get lucky once'."
Father Giles Orton, a Church of England curate from Derbyshire, in London to shop for "ecclesiastical supplies", says he is "just shocked and saddened".
But he adds, we "should be grateful" that it had not been worse.
Constantine, a 23-year-old student, says he was near Trafalgar Square when news of the attack broke.
"I saw the police start shutting everything off. I heard a lot of people talking. I have a cousin who works in Parliament and I live in Soho and I am a little worried about safety. Particularly LGBT safety which I am heavily involved with."
"I heard one man say 'this is why we need Donald Trump' which annoyed me," he adds.
Some MPs were earlier evacuated from the Palace of Westminster to nearby New Scotland Yard and Westminster Abbey, while others had to remain in the Commons chamber.
Pupils from Westminster School, next door to the Abbey, were in high spirits after being sent home early, although others said they had been in a state of shock when news of the attack broke.
Some of them wondered aloud why the school wasn't put on lock down like most of the other buildings in the area, including both House of Parliament and St Thomas's hospital on the other side of the Thames.
A man from Merseyside, visiting his daughter, who is a teacher at the school, said he was in the National Gallery when she texted him about the attack.
"It happens in any big city now," he says, "and any small city. I am not really surprised."
On Birdcage Walk, at the rear of Downing Street, civil servants were streaming out of imposing government offices after being sent home early; heads down, chatting to colleagues, refusing to chat to the media.
They trooped off towards Trafalgar Square in search of an alternative route home since Westminster Underground station was closed, melting into the crowds at Charing Cross and Embankment.
Beyond the police cordons and the TV crews it felt like any other day.