The attempt to reposition the UK as a tax shelter is going to make a very small group of people extremely rich but for the average UK citizen it won't matter one bit.
Why would a business decide to move the UK instead of the EU? They have to offer something that makes being outside of the single market worth it.
The UK is already much more business friendly than most EU countries (I haven't many companies rushing to move from the UK to France if they did not really, really have too, for instance) but not being in the EU/single market can be a serious drawback.
The EU also knows this and that's a reason the negotiations on single market access have been tense as too good an access without being bound to EU control would mean letting the wolf in.
Irrelevant?
Please back up your argument with more than just claiming that the state of financial services is irrelevant to the UK, and that it's about tax sheltering. I think you've been reading one side of a political argument for a long time.
The financial services arm of the UK is the major moving force behind Brexit in the first place, they did that knowing full well that the rest of the country would suffer. It won't take forever for people to realize this.
And with multi-nationals such as Shell moving to the UK the balance is shifting further away from where it should be, now the UK will act as a de-facto tax shelter in all but name because it can afford to offer these companies great terms, after all, they have nothing to lose.
Depends on where the money ultimately comes from. e.g. it would be smart for Russia to fund leave.
No surprise they wanted to separate.
It is happening as we speak.