London is a major global hub, and a hard Brexit wouldn't change that. But one of the best possible outcomes of Brexit could be a move toward real free trade beyond the faux "free trade" of the EU bloc.
MMT basically holds that governments have control of unlimited amounts of real wealth — thanks to money-printing power. But if this were really true, countries like the USSR and North Korea could simply create money until they became wealthy nations.
The Bank of Canada's official mandate to promote the “the economic and financial well-being of Canadians,” isn't compatible with the Bank's real mandate which is apparently to look out for the good of a small number of powerful banks.
While government spending re-allocates and distorts resources, it is not necessarily inflationary. Inflation really just stems from money creation and fractional-reserve lending carryied out by central banks and private banks — thus creating money "out of thin air."