The rich are busily withdrawing their money from the UK as fast as possible, and the closest thing to government policy right now is "er, we'll leave Europe but stay in Europe", so let's not get ahead of ourselves here.
That is a normal reaction in the near future, because London will lose its role as the European Banking Authority among other things... but in the long run, freed from the EU regulation, it only remains for the UK to become a big tax heaven among the likes of Switzerland and the British Virgin Islands.
Tax havens are so 2015. At a time when there is a rising impetus towards closing tax loop-holes the UK is going to try to differentiate its economy by exploiting them? It might just work, for London, but the UK is just too big to fly under the radar, and in any case it's difficult to build a domestic economy of the size of the UK on crumbs from the rich man's table ...
Are they? And why would they do that, fear of confiscation or something?