Having read your first post once again, OP, I now believe you are saying that you can't sell your motorhome because an HPI Check has shown it to be listed on the Insurance Companies Register. Is this correct?

This shouldn't, in fact, prevent you from selling it, you just might not get as much money for it when you come to sell it as you would if it wasn't on the register, that's all. If it hasn't been involved in being stolen and/or badly damaged in an accident during your period of ownership then it must have been listed on the register at the time you purchased it. Did you carry out an HPI check prior to purchase?

If it's an Insurance Company Register listing that's actually the problem then this is absolutely nothing whatsoever to do with the DVLA. You would need to attempt to find out from HPI why your vehicle is listed on the register and when it was put on there.

UPDATE

I did my own HPI check with the AA and it threw up what was an oddity. Yes the plate was listed by an insurer as a total loss. It was Cat B so should have been crushed. Not half as crushed as I was at this stage. HOWEVER, I noticed that the vehicle description said the write off was a JCB Loadall. I sent a query to HPI who have acknowledged that a wrong plate number has probably been entered by the insurer as they can see our van has never had other plates issued.They are investigating and it should all be sorted soon.

Thank you everyone who commented.