Thanks for this.

I am not discussing CGT 

I am discussing CGT on unrealised gains.

This is what happened to Roger Ver. 

He paid all his taxes correctly and left the US.

However, he left holding undeclared Bitcoin, which even at that time had made an unrealised profit.

He is being held in Spain for not declaring his Bitcoin and not paying CGT on his "unrealised gains" as of 2014. 

He is not liable, however, for the gains that BTC has made since 2014.

While the UK is a different regime, the same applies here. 

The only difference with BTC is you can take it in your head or on a piece of paper. You cannot take a second home with you.