Mick, if some establishments catered to smokers, an employee must be willing to expose him/herself to second hand smoke. Employees could be discriminated against if they were unwilling or incapable of working in a toxic environment. In the US, they'd holler at (Occupational Safety and Health Administration (OSHA). In the UK, there's probably a similar organization.

A private club could get away with it, but I don't know if an establishment open to the general public could.