Built at the beginning of the 20th Century, Admiralty Arch was
originally constructed as a memorial to the late Queen Victoria.
Miraculously, the Arch escaped damage during the Third World War,
despite the infamous nuclear attack on London by elements of the
Russian Confederation which rendered so much of the city
uninhabitable.
In the early twenty-third century,
Starfleet took possession of the listed building from the United
Earth Council, converting it into a dedicated Diplomatic Centre.
Over time the complex grew beyond it's diplomatic purpose as the
Administration Block was added, along with additional facilities for
education, recreation and operations.
By the 2380's the Admiralty Complex was Starfleet's largest Earth
facility after the HQ/Academy Complex in San Francisco - so when
that facility was extensively damaged by the Breen's sneak attack,
it was only common sense to switch operations in their entirety to
London.