If ever in doubt, contact an accountant. Give them the details, and the transaction records, and they'll figure it out for you. Depending on where you live, they could only charge you something like £100 for filling the necessary paper work (self assessment) or they might just charge you for consultation if that's all required.
Tax can be complex at the best of times, but when you come to Bitcoin, the various laws that have changed over the years, then tax can become very complex quickly. I prefer the piece of mind knowing I've had everything verified, checked, and filed correctly. It's one of the only times I quite like the idea of using a third party for verifying things. Plus, it takes a considerable amount of time off my hands each year.
However, generally as users have mentioned when you've bought into an investment, only when selling that investment does it become taxable. If you received that money as income, it would be a different story, and be liable to income tax.
I don't recommend getting tax advice on the forum, ask a professional lawyer instead, whatever that costs.
An accountant would be fine. They deal with this sort of stuff all the time, and know tax laws inside out usually.