Update:
The car has gone in to my local Sytner this morning for a "quality enhancement" or recall for the brake vacuum pump. The lady booking it in said that as a matter of course they will check the timing chain for any stretching or excess wear and will do a full replacement if necessary. I was surprised and quite impressed by this, especially as it's a 7 year old car with 80k miles on the clock and I've never taken it there for a service.
I'm not sure I trust that they will "check" it thoroughly enough though. I bet they just open the oil filler and prod it with a screwdriver. We'll see I guess.
Edit:
I stumbled across this when searching the forum:
http://www.e90post.com/forums/attach...2&d=1461352721
It looks like the do a "Timing Chain Test" whatever that is.