I don't think i ever mentioned that i found my spare wheel cover lying on the road one morning , when you bolt the cover over a wider wheel the cover is sort of spring loaded a little bit so you can get the nut on the carrier bolt . The cover was on the floor but the nut and bolt and alloy centre of the cover were all still on the truck . With no damage to suggest foul play i think the mild but constant pressure just made it let go . I removed the carrier and cut off the original bolt replacing it with a longer one the put a sleeve of copper pipe over the bolt to tighten up against . Slotted the alloy centre back into the cover and heaped araldite all around it .
Just remembered when i swapped the spare for a steel wheel i also swapped the wheel nut holding the cover on , the original alloy nuts were flared so might have held the plastic as well . There's a washer on my steel wheel nut now .