The bottom line with HPI or Volvo is that they themselves can't turn an RCD 1 compliant engine into an RCD 2 compliant engine if the emissions/noise requirements have become more strict between 1 and 2, so unless you plan to modify the engine to meet RCD 2 criteria, all they can do is give you the RCD 1 CE mark documentation, which won't be helpful here.
It's the act of importation that's the killer here, and it sticks in the throat that the same engines can be bought in boats already in the UK. The legislation intends to ensure that any boats brought into UK waters permanently meet current specifications, and it's just hard cheese that some of those boats would be older, used boats that will never likely pass the criteria for new boats.