You're talking about forked coins but the principle is the same, if you're trading or selling forked coins you've got to declare it to HMRC so they've got a clear picture of all your profits and losses in 12 months of cryptocurrency trading.
I'm no authority on UK taxation laws I've only been reading up on them lately. I'm advising people living in the UK to get advice from accountants and legal professionals before they get to their self assessment date.
Since you are pretty knowledgeable with UK taxing laws I think a lot of people here wants a clear answer regarding taxes on Hard forked coins or even if you have one. Since this is a big issue in the US if their hard-forked coins is taxable or not and what kind of taxes would even be considered for it. So I am also interested to see on what is the translation of the UK taxing authority when it comes to Hard forked coins in your country because currently US right now is still undecided about this topic.