All employers in the UK are required to abide by health & safety regulations and for the majority of aviation companies that have CAA & HSE compliant systems the systems are seperate with little overlap.
The overlap tends to be the requirement for a safety case under SMS and safety/risk assessments under HSE.
Anyone who thinks HSE doesn't apply in aviation may want to reconsider their view as the HSE people don't have much of a scenes of humour when investigating industrial incidents.
Miles