Do you have anything to substantiate that? All banks were publicly against Brexit and, working myself in the City (and working on dealing with Brexit), I hardly know any banker who was pro Brexit. Banks are large organisations that can deal with the complexity of Brexit by setting up subsidaries and moving people, but this is perceived as a hassle and a distraction, not an opportunity.

As for EU banking regulations, I disagree, it is quite the opposite. The EU has many broken banking systems (like in Italy) which prevents them for going too harsh on banks. The UK regulator has systematically gold pleated every EU regulation, imposed harsher rules and regulatory ratios, and the UK ring-fencing is the only hard ringfencing I am aware of (along with Switzerland). Most other EU countries imposed symbolic ringfencing between retail and wholesale banking activities.

Polish immigration is what caused Brexit really.