Many disinfectants and other methods when used in the field, (such as UV), rather than in a lab environment, have been shown to not be highly effective at addressing the presence of dry surface biofilms.
Dear Graeme, after biofilm formation on a surface, bacteria can survive a certain time. They also need nutrients to survive. The escaped bacteria from biofilm layer can also form another biofilm layer. In my opinion, if nutrients is not present and disinfectants, antimicrobials or UV treatment are applied, dry biofilm layer can not survive too much. The effectiveness of these antimicrobial treatments is also important. Especially in food contact surfaces. Some bacteria can survive in the presence of disinfectants e.g. Staphylococci and Listeria.