Well, after a short search, I've done it. I've gone and bought an E39 530i! The car had one owner, 86k on the clock and a full service history - mostly with BMW and more recently a local garage in Knutsford. It's on a '51 plate, silver, with black leather interior.
I'm looking forward to picking up the car tomorrow morning and giving it a good clean. I'll try and post some pictures after that. I'm sure this forum is going to be a great resource and experience for someone like me with their first BMW.