This article and others say the Corporation pretty much does as it pleases. There's a "conspiracy theory" that says that the City instigated Brexit to avoid EU jurisdiction.

You are confusing the City and the Corporation. It's a common mistake.

The City is not an autonomous enclave free from Parliamentary control.

Right, my bad, we're talking past each other.

The Corporation is some kind of acquisitive out-of-democratic-control alien dropped into the middle of London finance. OTOH the City is just another rich men's club I guess. Nice that its democracy for company-entities.