D.M.
Funny... I read the ideas the other folks posted to you first because I wanted to see what other folks thought about the joovy too. I also live in the UK so I know how space can be tight here and how much walking you need to do.
I've pretty much already decided on the Phil and Teds Vibe... but I keep hoping I'll find one that is a little less pricy. £500 (plus the cost of the doubles kit!!) is a little steep for me... but I'll cough it up if need be. I would definately check out Mothercare... there's a store in Bury St. Edmunds (plus if if you go on Saturday or Wednesday the market there is great!) The customer service was great... they showed me how the Phil and Teds would fold up super small (well... for a double anyways!)
Well... good luck with your stroller shopping!