Thanks to Sean and others for replying. Unfortunately, it was all a bit late for me, as I decided to leave it to the wisdom(!) of the dealer and to leave it.
I'm now going to get a oil and filter change to 5w30 at my local VW independent - they've got a decent rep, and (particularly as this isn't the first time they've let me down) the dealer won't be seeing any more of my money. That'll see me through to the next 'proper' service.
It's a pity, when I next change my car I will be reluctant to go VW as their dealer network is so poor - you'd think that VW HQ would wake up to that fact.