The MCA has published guidance (UK25/L002) which mandates that radar reflectors fitted inside liferafts, lifeboats or rescue boats must be individually UK-approved and tested to specified standards (e.g. EN ISO 8729 / IEC 60945).
Existing reflectors not complying may still be used until 30 January 2027, but after that date they must meet the required standards or new UK-approved ones.
Source: MCA.