A huge crowd is paying respect to the victims of yesterday's London attack
The memorial is being led by Mayor of London Sadiq Khan, who yesterday vowed the city would “not be cowed by terrorism”.
Huge crowds are now filling the famous square to listen to speeches and remember the victims of the attack.
Members of the public have used chalk to create messages of solidarity on the flood, including one which reads: "We are not afraid".
Three people were killed by terrorist Khalid Masood yesterday: PC Keith Palmer, who died stopping the attacker entering Parliament, US tourist Kurt Cochran, and mother-of-three Aysha Frade, who was killed as she walked to pick up her children from school.
READ MORE: When is the London terror attack vigil?
A memorial vigil is being held for the victims of yesterday's attack
Forty people were also injured in the car and knife attack, several seriously, including three other police officers.
Masood was shot dead by an armed Met Police officer at the scene just metres from the House of Commons.
Hundreds of people are gathering at Trafalgar Square to pay their respects to the attack victims
Cross-denominational religious leaders arriving at the vigil this evening
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The violent criminal had driven a 4×4 car across Westminster Bridge, striking a crowd including schoolchildren, before ramming the vehicle into a gate outside Parliament.
He then attempted to storm the building, fatally stabbing a police officer before being killed himself.
This is a developing story. Check back soon for the latest photos and information.