Disguising a London Underground ventilation shaft at the corner of the Mall and Horse Guards Parade is a memorial to police who have died on duty.
The blue hue of the column is reminiscent of the police blue light
After 13 years of campaigning and fundraising, and 20 years after the death of WPc Yvonne Fletcher - a killing which inspired the establishment of a memorial trust - the memorial is to be unveiled by the Queen.
It is a project started by film director Michael Winner, who donated £500,000 of his own money to the £2.3m project.
Mr Winner set up the Police Memorial Trust after the shooting of WPc Fletcher outside the Libyan Embassy in 1984.
He was determined that police who had died on duty should be remembered with memorials.
Since then 29 memorials to 33 individual officers around the country have been established but this is the first national memorial.
The memorial recognises the 4,000 police officers who have died while on duty in the last 175 years.
Most police officers who are killed while on duty die in crashes involving vehicles. Only a minority are murdered.
Mr Winner, who most famously directed Charles Bronson in the Death Wish series of movies, says he felt moved to set up the trust because of a lack of memorials for police officers.
"When WPc Fletcher was killed I thought 'nobody will remember her in a few years - no-one remembers police deaths'.
"It then occurred to me that the army, the navy and the air force, who fight wars for us, all have memorials.
"There's never been any public recognition of the police in this country and I set about putting this to rights - perhaps I am an odd candidate to do that."
Pages of the book containing the names of dead police will be turned occasionally
Police officers were "absolutely delighted" with the memorial despite some initial resistance," he added.
Mr Winner said: "At the beginning they were a pain.
"They were so paranoid - they thought that any public memorial to them would be vandalised.
"With almost every memorial I've put up, the police have said 'there's no point putting them up, they'll be knocked down tomorrow'.
"But they're all standing there - they've hardly ever been touched and they're all there."
The groundbreaking ceremony for the national memorial was performed by the Prime Minister, Tony Blair, and Mr Winner on 22 July 2004.
Designed by Norman Foster, with the help of Danish visual artist Per Arnoldi, it incorporates an underground vent, which cannot be removed.
Mr Winner praised the architect for his "immense help", not only in designing the memorial - a gift from the architect to the trust - but also in "getting over all the hurdles of planning".
Roll of honour
Clad in marble and covered in creeper, inset behind glass on one side is a book with the names of 1,600 officers police officers slain on active duty.
Pc Ian Broadhurst was shot while on duty in Leeds on Boxing Day 2003
As well as WPc Fletcher, other officers mentioned in the special roll of honour include:
Pc Ian Broadhurst, who was shot while on duty in Leeds on Boxing Day, 2003 by American bodybuilder David Bieber;
Special Branch officer Detective Constable Stephen Oake, who was stabbed to death trying to stop an al-Qaeda terrorist during a raid in Manchester in 2003;
Pc Keith Blakelock, killed in the Broadwater Farm riots in Tottenham, north London, in 1985;
Pc Sidney Miles, who was shot in Croydon, Surrey, in 1952 - Derek Bentley was hanged for his murder.
The pages of the book will be turned occasionally, with more names added when necessary.
Perpendicular to the marble vent is a glass wall, lit with a blue hue representing the blue light that was traditionally outside police stations to show officers were always on duty.