Hi Old Geezer,
You would need to identify whether any asset was acquired when you made this payment of £20,000.
Ultimately, a Capital Loss can only be realised upon the disposal of an asset, whether that's a property, shares in an investment company or interest in or right in or over an asset.
You will need to identify what you actually acquired (if anything) and when this asset was disposed of to allow you to identify if any loss arises and when the disposal took place.
CG12700P - Introduction and computation: occassions of charge: disposal of assets: contents
Thank you.