Hello there Starwoz, I hope you can get some help with this but it is a difficult piece to assess. It's also true that you haven't helped your case with your original post which contained a number of red flags (using someone elses pics, getting a very pertinent fact wrong about the number stamp, and using the wrong terminology 'U Grade').
The story about buying it from a car boot also means you have no provenance (I also think it is fair to say that the UK wasn't exactly a hotbed for bootleg production and so finding any vintage Star Wars bootleg at a UK car boot sale would be extremely unlikely).
This doesn't mean it's not genuine but I think it would be difficult proving that this has age and wasn't made last week. Probably the few people who could help authenticate it would be those few who already own one and could do a very close comparison with yours and the one they have, perhaps a weight comparison, looking at mold lines with a magnifying glass, and maybe the base that yours seem to be standing on. Joseph Yglesias is considered the leading expert on vintage SW bootlegs and if he came out and said yours was genuine then I think that would be enough for anyone. I will forward him a link to this thread and see if he can help you.