Marcus,
I also live in the Manchester area and have looked at buying a 550. Unfortunately, pressure of work, three young children and repeated bad choices of six numbers on a Saturday night (!) have put the plans firmly on the back burner.
Rather than import straight away, have a look at, in no particular order
Martin and Walker
have http://www.904gts.co.uk/
Classic Roadsters
http://www.classicroadsters.co.uk/
I have spoken at length on a few occasions to Martin Craven and he has sent me lots of information about their 550 product. A real enthusiast. I have some of their pictures as screen savers.
One day...
Tygan Motor Company
http://www.chesil.co.uk/intro.asp
I saw that Chesil were making a 550 replica, about a year ago. The North West agent was based in Knutsford, I think. I heard rumours from the US (on this site)that Chesil were perhaps having financial problems and now Tygan have bought Chesil's assets. There is a link to a Northwest agent, but not idea where they are based.
Thruxton Sports Cars
http://www.thruxtonsportscars.co.uk/
Importers and distributer for the Beck 550.
Good luck.
If they offer you a 'Buy One, Get One Free', give me a call...
MARTIN