John, I would have thought it was how many employees you have overall rather what each individual does....if one of your forecourt staff injured themselves passing "through" your workshop then Health and Safety would look at what measures you had in place to prevent/lessen that risk. ie training/posters Not sure if I've answered your question but hope this helps..
Have you got a "Health and Safety Policy Statement" if you haven't I can fax you a copy of ours that you could use Dave