RE: As I said12 Jan 2021 21:22
Copied from HMRC’s website:
Using losses to reduce your gain
When you report a loss, the amount is deducted from the gains you made in the same tax year.
If your total taxable gain is still above the tax-free allowance, you can deduct unused losses from previous tax years. If they reduce your gain to the tax-free allowance, you can carry forward the remaining losses to a future tax year.
Reporting losses
Claim for your loss by including it on your tax return. If you’ve never made a gain and are not registered for Self Assessment, you can write to HMRC instead.
You do not have to report losses straight away - you can claim up to 4 years after the end of the tax year that you disposed of the asset.