I reported it to the local police station (I think, if switchboard put me through to the right number - a pleasant man took the details, but there isn't much they can do). Hospital security may have some CCTV footage which they will look at tomorrow, but I couldn't see a camera near where the bike was.
I've tried and failed to get a picture here - it's a Colnago World Cup (back and white cyclocross bike), with eggbeater pedals and low saddle - can't have been that easy to cycle off on.
I'm just looking at the insurance now...