@hazardwarning My guess is that once London is no longer within the EU, there will be an exodus of some firms to Dublin, Brussels, Paris, and Frankfurt, particularly in the financial sector. Dublin may be the big winner, as an English-speaking EU capital. Nothing dramatic is likely to happen short-term, as quite apart from everything else, there are lease agreements for office space that must be adhered to.
Then you have manufacturing: Unless a deal is worked out, Nissan's plant in Sunderland is likely to lose out to Renault plants on the Continent, as Renault and Nissan are linked. Then you have Mini, owned by BMW, who may be interested in moving at least some manufacturing to BMW plants for European consumption.
It's going to be interesting, that's for certain.