Gels are posh and quite often “game”, they are the type who feature in the poems of John Betjeman –
Miss Dunn is undoubtedly a gel.
Googles
I’ve never heard them called that, but yes, apparently so.
Ook?
That example doesn’t parse for me - it sounds like a regionalism. Generally, ‘twee’ is slightly derogatorary, and typically would describe the same things that American tourists would consider ‘quaint’ 
I don’t know if it’s a medical distinction, but verucas are associated with feet (and with unhygenic swimming and shower facilities…)
Absolutely Ook!
Hmm. I, as an American, was unaware that ‘gone all pear-shaped’ was British slang. It’s certainly a phrase that I’m familiar with, and I don’t think I picked it up from British entertainment. But maybe it’s also a New England thing.
“Twee” is a real word. It apparently stems from a childish pronunciation of “sweet” (or possibly “treat”). Basically means “affectedly dainty or quaint” (Pocket Oxford dictionary).
I believe a verruca is what we would call a Plantar’s wart–the kind of wart on your foot that grows inward?
It was Milton Keynes. At the beginning of the book it’s laid out how the angel Aziraphale and the demon Crowley – senior representatives in the UK of Heaven and Hell, respectively – have decided (without their superiors’ knowledge or permission) to make their work easier by compromising. Each allows the other a sphere of influence to work without interference. “Crowley had Manchester, while Aziriphale got the whole of Shropshire. . . . Nobody was sure who was responsible for Milton Keynes, but they both took credit for it anyway.” Footnote for Americans and other aliens: Milton Keynes “was built to be modern, efficient, healthy, and, all in all, a pleasant place to live. Many Britons find this amusing.” See http://en.wikipedia.org/wiki/Milton_Keynes.
I know a jelly baby is a kind of candy, but I don’t think I’ve ever seen one. (On Dr. Who, I never caught a closeup of the candy the Doctor was eating.) Is it something like a gummi bear? Or more like a gumdrop? Or a jujube?
That site still doesn’t make clear what they look like or taste like.
Actually it’s the M25 which circles London.
Both the M25 and Milton Keynes are running jokes in Britain. If you use the M25 regularly it is easy to see why people take the piss (and why it might well be the work of Satan). But Milton Keynes, what’s funny about that?
Jelly babies are coloured chewy sweets in the shape of tiny people.
Jelly babies are an odd confection; they are, as the name suggests, smallish, notionally fruit-flavoured jelly confections, but the texture is not like other jelly sweets; whereas gummy bears etc have a sort of springy, chewy resiliency to them, jelly babies have more of a soft bite texture, with a sort of firm sugary crust. Imagine a rather unusually soft, large jelly bean and you’re not a million miles away.
Conversation between 2 work colleagues from about 15 years ago I still remember, strangely:
Helen: Would you like a jelly baby?
Stephen: Oh, go on, but make sure it’s a boy one.
Helen (puzzled): Surely there’s not that much difference?
Stephen (smugly): No, but there’s that much more jelly.
Ba da boom.
Look, mate, are you trying to tell me I don’t know my own uncle’s name?