The manufacturer of the cooker will have siting information such as "Adjacent side walls which project above hob level, must not be nearer to the cooker than 150mm and should be protected by heat resistant material. Any overhanging surface or cooker hood should not be nearer than 650mm."
The installer must install in compliance with the manufacturers specifications, in the absence of such data the installer will have to use his experience of other similar fittings combined with his own judgement.
As a professional the installer (as a company and as a certified individual) is legally responsible for the way he fits things, his decision on the safety of a fitting is his responsibility whether the aspect is covered in law or not and this liability cannot be signed off.
In a time of universal deceit - telling the truth is a revolutionary act. George Orwell
When the debate is lost, slander becomes the tool of the loser. Socrates