Does anyone know where I could get hold of a reflective jacket like the one pictured on this website http://www.vorsteh.se/

Would be very useful when out working my GSP in open areas

Ive had a little look on ebay but no joy

Have you tried equafleece? I often use the "Spot the dog" bandana thingy for my Sussex Spaniel because, being brown, she tends to blend in with the background and I often lose sight of her. http://www.equafleece.co.uk/ProductList.aspx?category=1

Countrymun has something similar.
Waggers version

I'll keep my eyes peeled for more.

Found one at Cabelas that is as streamlined as the one in your link. They're in the US but they'll ship over here and the coat is about £7 at today's rate and easily popped in an envelope.

I got mine from the US from dogs unlimited http://shop.dogsunlimited.com/list.asp?d=32&p=1 They were very helpful with measurements etc. and shipped in a couple of days.  Could not find anywhere in the UK that sold them.  It is the Tummy Saver