The Panama Papers showed this is how London (or the 'The City of London' to be precise) has stayed financially relevant since the fall of the British Empire.
Do you have a citation for this? How would this be possible?
The fall of the British Empire begins with World War 2 and is mostly finished by the independence movements of the early 1960s. Yet "The City" was only deregulated in 1986 under Thatcher.