Well after a lay down in a dark room, and really not wanting to go to a dealer or tyre fitter, I found a mate at work that owned a Snap on impact driver.
After loosening the other three locking wheel nuts first I went to work on the stubborn one. Forcing the gun and the key socket firmly against the nut then fired it up. After about 5 mins nothing was happening, so I tried agin then it finally went.(15 minutes later)
I am so relieved at this. Now I can clean the wheel and fit the new set of locking wheel nuts correctly.
Thanks Gents for all your input, this forum is definitely a fantastic resource, with very helpful members.
Best Regards
Keith.