Assuming the application is to bare solid timber that is a minimum of 12mm thick, approval is sought from building control prior to application, you could consider Zeroflame Fire Retardant Treatment for this application. This can achieve Euroclass B s2 d0 (replaces UK Classes ‘0’ and ‘1’ BS 476 Part 6/7*).

This cannot be used on mdf, osb or plywood to acheive Euroclass B.