Some banks are already backtracking on their promises of leaving London for Paris or Frankfurt [1] [2].
[1] http://www.ft.com/fastft/2016/06/30/hsbc-rules-out-leaving-l...
[2] http://www.independent.co.uk/news/business/news/hsbc-headqua...
[1] http://www.ft.com/fastft/2016/06/30/hsbc-rules-out-leaving-l...
[2] http://www.independent.co.uk/news/business/news/hsbc-headqua...
What HSBC have said is that they may move about 1,000 jobs to Paris. That's because those jobs are tied to services that by law must be provided within the EU legal and regulatory environment. When London leaves that environment those jobs will go, not just at HSBC but across our financial sector. See my other larger post on this page for further details.