have you thought about wiring it like they do on race bikes jubillee clip around sensor wire around pipe and back of jubilee clip stop it turning .Or is thread knackered

I think I may have it sorted. time will tell. I think part of the thread had something wrong as i got a new spanner and managed to get a fair bit more turn out of it than i was with the old tool. Almost like something was blocking in the actual pipe. I wouldn't have known any different as the head appeared to be completely flush when i was tightening before. Something just gave when i used the new spanner. I'll see how it goes.

sensor out lambda plug in job done

I did this when my sensor fell out on the nexus, while I waited for a new bolt to come, and yes it's a 10p piece