To my great relief (and stgpcm's too, I suspect) the referral letter did seem to do the trick, given that, despite the scrolling LED signs saying "Your expected time from arrival to seeing a doctor is currently three hours" (which actually wouldn't be at all bad for a Friday night), I was triaged before half an hour had elapsed, and then had to wait only another hour or so to see the the lovely Dr Tim.
Dr Tim is of the opinion, having poked my chest and listened to my lungs, that "there's definitely some gunk in there" — never let it be said that modern medicine is jargon-infested — and given that, apparently, virus-nibbled lungs don't consolidate in the manner of bacterium-banqueted ones, he's put me on a week's worth of oral erythromycin; 500mg, four times daily.
He also thinks that my leg problem is a mere superficial thrombophlebitis, not at all so bad as a DVT would have been, but, as he said, "it's always better to err on the side of caution." Therefore he wanted blood tests done, so I've been thoroughly phlebotomised (I'm thinking of having my circulatory system put on the IUCN Red List, it took such efforts to hunt down a viable vein). I've had an ECG. I'm back on Clexane injections (I have to attend UHC for another on Sunday morning). They'll be calling me on Monday for an ultrasound scan appointment.
All said, though, apart from my chest and leg aching, I feel pretty fine. Thank you for all your support and good wishes!