The biggest subsidy is the presence of government/civil service and royal "machinery", which ensures a steady flow of public money into the area before we even

The biggest subsidy is the presence of government/civil service and royal "machinery", which ensures a steady flow of public money into the area before we even look at the vast amounts spent on London's infrastructure. Much of British transport infrastructure is also designed to feed people into London (although London is less bad for that than Paris which is the hub of nearly all the French rail network.) The Channel Tunnel certainly does. Even the motorway and rail networks of Wales do to some extent.