Thanks everyone. Taking all the great advice given, especially from W3ATT with the link to the K0BG site (which is brilliant) I now have a 40m mobile that has an SWR of 1:1.1 with X=0 (ish) with just a bit of tweaking and the addition of a coil. So not only have I got an antenna I can use, but I’ve learnt a great deal. Now the boring bit of tidying it up!
I think I got the best of both worlds. Trimming off 2" and leaving about 3" inside seemed to be as good as having none inside. So I still have enough adjustment to get down to the beacons but probably not CW… 73 John