The British Occupational Hygiene Society (BOHS) Covid-19 Working Group developed a control banding matrix to provide guidance for employers and others to help assess the risks of Covid-19 infection during the pandemic. The matrix was based on occupational hygiene principles and the judgement of the occupational health practitioners involved; since objective data on workers' exposure were unavailable. Users of the matrix identify one of five exposure categories based on generic job descriptions and example occupations, and these categories are linked to generic guidance on interventions at source, on the exposure pathway and for individual workers. The risk matrix was published on the BOHS website and the guidance has been downloaded more than 2000 times. The matrix has had limited evaluation for reliability, but the data suggest that the highest exposure ranked jobs were associated with higher age-standardized mortality in Britain during the pandemic. However, there was considerable variability in exposure assignments between assessors, which underlines the need for the control guidance to be precautionary. The BOHS calls on academic researchers to undertake further work to validate the reliability of the tool.