So what i did was along the lines of Pauls suggestion.
The vac form when its fitted sits in a slight recess on a ledge about 10 thou deep and 25 thou wide so it flush with body.
I coloured the ledge in with a felt tip pen , cut the vac form to about 3mm to big all round then care fully cut othe longest side to the line in the vac form. Located that line on its corresponding ledge on the panel and taped the whole thing in position. I then used tape again on the outside of the vac along the edge of the black marked ledge that showed through so i transferred the black edges to the vac with tape...then cut the vac along the tape.....and it worked
the vac is held in place with .5mm or 12 thou rivets so now i need to drill the vac through and on to the ledges. its not going to be perfect as drilling by hand a 12thou rivet on to a 25 thou ledge means i have about 6 thousandths of an inch between the hole in the vac and the edge of the vac.
Lets face it thats not really going to happen

but this is a learning build for more expensive and complicated builds later...(see below) and i am really happy with what i did last night , just got to do the windscreen and side windows now ....lol
This arrived in the post yesterday
just look at the vac form and rivets on that

This will be my effort to redeem my self from the failed Revell E-Type last year ....
I have been really lucky with this jag and the Ferrari i ordered last month as both have arrived without import duty and tax saving me about £150 each !!!!!
The Ferrari has virtually no vac but it has spoked wheels,
what i need is a car with alloy wheels and no windows
Just to complicate things , someone has asked me to build them a Spitfire. I sort of think its a subject i have done, seen the film and read the book but they want it in desert camo and thats something i haven't done so...maybe.