Within the EU framework as a citizen you could argue that the FCA measure of a wholesale no to crypto currencies is not proportionate nor in law nor in regulations.

But the UK citizens opted to get out the EU.

Indeed you could argue that, and could probably get away with that in European court where bank accounts must be provided, consumers have rights, and courts side with consumers whose rights are trampled.

But the British regulator will argue that the law backs them up, and the courts in Britain won't take on London.

Where the subtlety is coming from is that the British regulator has accepted the banks' anti-competitive behaviour - London is Britain is banking. So the banks and regulators will all agree that crypto is a threat and they don't want anything to do with it.

Once that agreement is found, the policy is crafted to suit the decision. That's what we see in the FCA letter, using the language of mandarins.

Sadly, what they don't realise is that they have sewn the seeds of disaster - decades ago, and now those plants are growing strongly. I actually think it is way past the possibility to put those weeds back in order - I expect British banking to collapse from the inside in the next decade. People will blame Brexit. But it's really well before then.