People do not just moving businesses for purely political reasons, there has to be concrete economic reasons.
I actually think that the UK may be less regulated than EU exchanges and that may stay in order to keep the UK more attractive.
If you do not list any real economic reasons, I think this is just scare talk.
London is one of the biggest (or rather the biggest) hub for EUR-denominated trading and AFAIK they're only allowed to do so because they're EU member. There's also the practice called passporting: Bonds, Insurances etc that are regulated in one EU country are allowed to be sold in all EU countries. The UK had the most favorable regulations for those bonds, so a lot of them moved to London. Now that London might soon not be part of the EU any more, the banks at least need a residence in a EU member state. Some might consider to substantially reduce their London operations.
— Ben Thompson (@BBCBenThompson) June 24, 2016
Sources at Morgan Stanley tell BBC it's already begun process of moving 2,000 London based investment banking staff to Dublin or Frankfurt
lack of a free trade agreement with europe comes to mind.
Stability plus the fact that Frankfurt is already a major financial hub, and that Germany is a major driver of the EU economy.
Funny how the leave voters of fear and spite are now here talking about punishing the uk out of spite :)
And yes, France is now a bigger economy than britain, and it's just been a few hours now.