My understanding of UK tax on Bitcoins for individuals (not a company) is that any profits when Bitcoins are sold for GBP are subject to Capital Gains Tax.  There is currently an annual tax-free allowance of £11,110.00.  So unless you are a whale or an incredibly lucky investor you possibly won't pay any tax on Bitcoins sold.  I am a Software Engineer not an accountant nor tax adviser so please don't rely on my understanding.