Google HGV inspection training. There is more than one company offering these courses.
If you are planning to do your own inspections then you need to provide certain facilities.
assets.publishing.service.gov.u … hicles.pdf
Your keen mechanic will have to work to the standards in this following link at an absolute minimum and obviously appreciate the significance of any defects he discovers. He needs to understand that his signature on the inspection sheet is a legal declaration and he can end up in jail if he is proved to be negligent or corrupt.
assets.publishing.service.gov.u … manual.pdf
The keen mechanic will need to have an understanding of how air brake systems work since you are presumably going to be expecting him to carry out rectification work?
Above assuming we are not talking about a trained HGV / PSV mechanic.