I looked into this before.
Any profits are subject to CGT. The tax-free allowance for it is £12300 pa.
If you’re a higher or additional rate tax payer you’ll pay 20% on the excess.
Otherwise if the excess is £x in the tax year apply to £x whichever tax rate (taxable income + £x) falls into.
Example
Your taxable income (your income minus your Personal Allowance and any Income Tax reliefs) is £20,000 and your taxable gains are £12,600. Your gains are not from residential property.
First, deduct the Capital Gains tax-free allowance from your taxable gain. For the 2020 to 2021 tax year the allowance is £12,300, which leaves £300 to pay tax on.
Add this to your taxable income. Because the combined amount of £20,300 is less than £37,500 (the basic rate band for the 2020 to 2021 tax year), you pay Capital Gains Tax at 10%.
This means you’ll pay £30 in Capital Gains Tax.
Don’t be a tax cheat lol.
If you’re determined not to pay tax but want to stay within the law you can try spread betting at one of the online firms eg IG Index.
If you claim it’s from winnings at sports betting the IR can demand to see proof or evidence of bets you’ve made, including records they’ll expect you to keep. In reality they’re unlikely to bother with modest amounts but anything in 5 figures or over is always suspicious and smells of money laundering.