Drainage lintle Back filled with soil

[jaimeontour]

We have has damp in our kitchen at the under sink unit point...thermal imaging shows cold air at skirting point ,buildings insurance say its rain water ingress as they did a chlorine test and no salts found.Builder still says its a washing machine leak.
I dug outside adjacent to sink,down to the waste pipes and found that a lintle runs over them ...digging deeper I found the void below the lintle is back filled with soil with a shingle under the pipes.
Looking At building regs part H it says that a lintle piped drainage should have a rigid sheet either side of the void to stop vermin and back fill and that the void itself needs to be filled with a compressible sealant to prevent entry of gas.
I asked the builder and they said they are not qualified to know the regulations and we should speak to the Building insoector (private company ) as they signed it off.
Do any of them have qualifications?
I await the NHBC man also with no qualifications.