Thanks guys - I wanted something slightly more business-y than the outdoor shops but I completely forgot about Selfridges and they have a pretty good luggage department (I'm UK domiciled ...)

In the end I went to Victorinox but couldn't decide what I needed wanted so I left empty-handed. Not the end of the world but I'll do a bit more window-shopping before making a choice (And I'll have to stick with an over-the-shoulder duffel for now.