The body of murdered Pc Keith Palmer has begun a final journey through the city he once protected as thousands of police officers lined the route of his funeral cortege.
The 48-year-old was stabbed to death by Khalid Masood as he carried out his duties on the cobbled forecourt of the Palace of Westminster on its journey to Southwark Cathedral, in central London.
Pc Palmer's coffin will travel along 2.6 miles of the capital's usually bustling streets, avoiding the scene of last month's atrocity on Westminster Bridge, to arrive for the 2pm ceremony.
A floral tribute left on top of the hearse read: "No 1 daddy".
Around 50 members of Pc Palmer's family including his wife, child, mother and father, brother and sisters will attend the cathedral service, which will be led by the Dean of Southwark The Very Reverend Andrew Nunn and followed by a private cremation.
Met commissioner Cressida Dick, the first female head of Scotland Yard in its 188-year history, will also attend the funeral in her first public engagement in her new role.
The Met said more than 5,000 officers from the force and across the country were expected to gather in central London for the service and to line the route, which has seen dozens of roads closed to traffic for hours.
Columns of officers in dress uniform, many with service medals pinned to their jackets and wearing white gloves, lined up near the cathedral as on-duty colleagues involved in the large security operation stood guard.
Members of the public also began to line the barriers several hours before the service began.
Chief Constable Sara Thornton, head of the National Police Chiefs' Council, said the scale of the funeral will be unprecedented as officers hold a two-minute silence at 2pm.
She told the BBC's Victoria Derbyshire Show: "I don't think we will have ever seen a police funeral of this size.
"Officers from all over the country are coming to London to join their Metropolitan Police colleagues to line the route.
"We all want to pay honour to the ultimate sacrifice that Keith made."
The Queen gave permission for Pc Palmer's body to rest in Westminster's Chapel of St Mary Undercroft, an honour normally reserved for senior figures.
Ms Thornton said the gesture had had a "tremendous impact" on police as they go about their duty.
She said: "The fact Keith has laid in rest in the Palace of Westminster is a sort of acknowledgement on behalf of the whole country of the sacrifice that he made but also the job that officers do day in, day out."
Full service funerals are normally only held when a police officer or member of staff dies while they are carrying out their duty, Scotland Yard said.
The last full police funeral for a Met officer killed in the line of duty was in October 2013 for Pc Andrew Duncan, who was killed the month before after being hit by a car while checking vehicle speeds in Sutton, south London.
Pc Palmer's name has been added to the roll of honour and remembrance at a ceremony at the National Police Memorial on The Mall, in central London, complete with a guard of honour.
Steve Lloyd, of the Police Roll of Honour Trust, said: " We hope that knowing their loved one's name are to be forever remembered will bring some small comfort to the families of the fallen officers."
Four other innocent people were killed and dozens of others injured in the 82-second atrocity in Westminster on Wednesday March 22, which ended with Masood, 52, being shot dead.
Andreea Cristea, 31, Leslie Rhodes, 75, Kurt Cochran, 54, and Aysha Frade, 44, died after Masood ploughed into pedestrians on Westminster Bridge.
Ahead of the service, Labour leader Jeremy Corbyn said of Pc Palmer: "He was a lovely man, we all saw him every day when we went into the gates of Parliament.
"He was there with a smile, with a wave, always talking to tourists, always talking to visitors, always unbelievably polite and courteous - a real, good public servant of the people in Parliament.
"He died defending our Parliament."
John Louthrey, 62, a retired chef and bell ringer at St Leonard's church, Streatham, south London, said he had come to Borough High Street before dawn to pay his respects.
Draped in a Union flag and holding a sign, he said: "I'm here to pay my respects to Keith Palmer and the officers of the Metropolitan Police.
"We pray for the police to keep us safe and we pray that they are kept safe and we pray for Keith Palmer's family."