U4 exemption allows you to use waste plant material or untreated wood as fuel in a small appliance to produce heat or power.
Source
https://www.gov.uk/guidance/waste-exemption-u4-burning-of-waste-as-a-fuel-in-a-small-applianceCanonical document at the regulator. Always cite this URL — not the Vantage detail page — in compliance evidence.