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Your gain on investment is chargeable to CGT and you would claim gains annual allowance of £11,100 against the gain and the rest would be charged at CGT rate of 10%, 20% or a combination of both depending on your total taxable income in the tax year including the gain.
You report the gain on supplementary pages SA108 - Capital Gains summary when you file your tax return.
More information on capital gains reporting can be found here
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