Yesterday, the officer's coffin was draped in the flag of the Metropolitan Police as it was taken to a chapel just a short distance from where he died.
PC Palmer, 48, rested at St Mary Undercroft in the Palace of Westminster for 24 hours before his funeral at 2pm today.
The special distinction of a “lying-instate,” normally reserved for senior royals and politicians – went ahead after the Queen gave her consent.
Police officers protect floral tributes left ahead of PC Palmer's funeral
Thousands of mourners have already lined the streets with their personal tributes
Yesterday 12 police officers in full dress uniform formed a guard of honour as eight pall bearers in tail coats brought PC Palmer’s coffin to the chapel.
Today, more than 50,000 mourners will be joined by thousands of police officers representing every force in England and Wales to say a final farewell.
The funeral will also be attended by up to 50 members of PC Palmer's family including his parents and his young daughter.
Officers arrive for the funeral in London
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Floral tributes blanket the street near the site where the PC died
During the service, PC Palmer’s coffin will be received by the Dean of Southwark, The Very Reverend Andrew Nunn, who will also welcome the congregation.
Prayers will be taken by Reverend Prebendary Jonathan Osborne, Senior Chaplain to the Metropolitan Police Service.
Chief Inspector Neil Sawyer, who worked with PC Palmer in Bromley Borough and the Territorial Support Group, will then deliver a tribute to the fallen officer.
The service will feature a number of Hymns, including "I heard the voice of Jesus say" written by Horatius Bonar.