Well, Just in case anyone is interested here's what I did.
I phoned a place called inside out 4x4 who is based only a few miles from where I live and luckily enough they had a P38 in for breaking with front end damage. I nipped over there and managed to remove the rear bumper to reveal a very nice steel structure inside with only surface rust so I paid £50 and took it home.
The steel bits are only screwed into the plastic bumper with 4 bolts and 2 screws so I soon took the steel bits out, cleaned them up, painted them with some gloss black chassis paint then re-fitted it all into my original green painted plastic shell.
New brackets on the chassis ensured a nice fit and with plenty of copper grease on the bolts it was secured back into place. A simple task in the end and it looks as good as new.
If anyone needs a very good condition, black plastic bumper shell with Epsom green inserts, I have one going spare.
Thanks for the help
Craig.