Jason-I am in the states, and cannot offer a source. But, I can suggest you think about doing what I did for exhaust on my 40. I have a 351 Cleveland, so none of the systems out there came close to working on my car. I found a race shop in my city where the owner had done lots of headers for drag cars, road racers, etc. He scratch built my system, on my car, with true cross-over and equal length pipes. It is one item that really gets comments from people when I open the tail section. I had it ceramic coated, and it has held up really well. As you are in the UK, the home of race car fabrication, I would think with some exploring, you could find a reputable fabricator to custom build a system for your car, using pictures and a few specifications. And, I would bet it would cost you the same or less than the bolt-on systems out there. You can choose your mufflers, your finish (chrome or ceramic), clearance around certain suspension or bodywork, etc. Just a thought. This approach worked for me, and was alot less than I thought it would be.
Good luck-Jack