Ok, here is an update on the spring discussion -
After reading your comments and weighing up the options, I decided to contact 'Trick-Bits' to have one made. I spoke to a guy called Ian, who was very helpful.
I sent my old spring to him for exact measurement and he set about making a new one. My old spring was away for five days, returned to me via recorded delivery. Exactly two weeks later the new one arrived, powder coated in yellow.
It's now been refitted and I have been trying the bike out - what a difference! The bike doesn't sit down at the back as much and the whole thing seems alot smoother and controlled. (This is compared to winding the spring up with the bottom adjustment ring).
Although, I haven't had chance to really put the bike through its paces - its a case of so far so good !
If any of you are thinking of uprating your spring, give Ian a ring, he very helpful and the product is top class !
I hope this is of use.
RR