It's also available from YYZ, if that helps anyone on here.
Traveloguy - I linked to a post from a recent UA MR to DME thread that seemed pretty clear that you don't need a visa if you're doing an immediate turnaround. I'm still trying to work out why some ITA queries are returning just an 11UKP tax element for >24 hours at LHR (see my post on that thread - any help welcomed!)