I don't think the Government can actually do anything about it. As far as I am aware we have free trade and for any item to be illegal to trade i.e. firearms, drugs, first they must be defined as illegal.
I am not aware of any UK rulings on Crypto currency defining it let alone making it illegal to trade? Please tell me if I have missed something, I know the scene is moving at a fast pace and I know they are concerned regarding money laundering and tax evasion.
I don't envisage armoured trucks full of cash in the field
The only thing I remember hearing so far that may be relevant is that any profits made from cryptocurrency related activities are liable for capital gains and income taxes etc. so watch out for the revenue turning up at your car boot sale