The Changing of the Guard ceremony at Buckingham Palace has been cancelled on Wednesday to redeploy police officers, the Ministry of Defence say.
A Ministry of Defence spokeswoman said:
"The decision has been taken in order to release the police who would otherwise be dealing with the road closures."
The New Guard, the RAF Queen's Colour Squadron, were due to process to the Palace from Wellington Barracks to replace the Old Guard in the traditional ceremony which attracts hundreds of tourists.
However, there was also only an administrative move.
The new guard took over from those on duty without the usual pomp and ceremony of marching troops and military bands.
The ceremony was also cancelled at Windsor Castle. Soldiers from the 1st Battalion Coldstream Guards were ferried to the Queen's Berkshire residence by bus instead of marching up from the town's Victoria Barracks.
The House of Commons authorities have also announced that the building is being closed to non-passholders today.
This comes as a response to the attack in Manchester, when a device was detonated during a concert, killing 22 and injuring 59.
Police have named the bomber as 22-year-old Salman Abedi, who is believed to have travelled to Syria and had "proven" links with the Islamic State (IS) terror group.