What does "SDH Autos" refer to in the context of vehicle inspections, specifically regarding the MOT inspection manual for private passenger and light commercial vehicles?

The term "SDH Autos" is not mentioned in the provided MOT inspection manual for private passenger and light commercial vehicles. This suggests that it may not be a standard acronym used in this context. Without more specific information or additional documents, it's challenging to determine what "SDH Autos" specifically refers to.