The reason for carrying a tin of paint in two carrier bags on public transport is the idea that the bags will contain any leaks from the tin. No messy spodges on the buses for people to slip on! It is not, however enshrined in health & safety legislation but is a policy adopted by many transport companies including the one I work for. I worked for many years on cross-channel ferries and there were never any fast rules about the carriage of small quantities of paint or similar materials other than the requirement that they be properly stowed in the vehicle. A different matter for lorry loads of hazardous substances, which were still permitted on the ferry with the correct hazard warning labels, but were, where possible, placed at the ends of the ship rather than the middle. This being so that any problems could be more easily contained. cheminot