So three unclued entries and a connection between them (visible in the final grid). There are also 2 currently relevant words to find making a total of 54 letters to highlight. Now that’s a lot.
No subtle variations in the clues this week, though there did appear to be a lot of american words refernced in the puzzle, which was peculiar given the theme (see below). Lots of other obscure words added to the challenge, many used as wordplay and this led to quite a long time explaining each clue. One, as often is the case, a short one 38dn has so far eluded me, though the solution is a Canadian word. Whilst many answers were obvious, their derivation required a good thumbing of Chambers.
As to the three unclued entries, all fairly straight forward:
STREET LEVEL
EARLS COURT
UNDERGROUND
In that order vertically through the grid.
So what could connect one to another – a diagonal ESCALATOR. This it turns out was the first escalator on the London Underground. A quick search on google yielded this information and a news item from the 13th September 2011 relating to trains not stopping at Earls Court due to emergency escalator works. How London’s transport system has changed, even in my lifetime!
The other 2 words to highlight were OCTOBER and CENTENARY.

So the end game was all very neat, tidy and simple to spot, but the obscurity (to me anyway) of some of the words used made this a little harder than the average.
Key:
Rev (Reverse) DD (Double Definition) * (Anagram) Underline Clued Definition
ACROSS
1 Practices no longer hiding physician’s birds in Africa (6)
Ures (Archaic form of practices) around (hiding) MB (Physician) = UMBRES
5 Refuse to wear old German shoe with decorated pattern (6)
Bran (Refuse – my opinion of bran flakes too) around (to wear) OG (Old German) = BROGAN
12 Even mother provides substance to be injected (5)
Ene (even) + Ma (Mother) = ENEMA
14 Whipped cream I put on cold and applied to acid from some grapes (7)
(cream)* [indicated by whipped] + I + C (cold) = RACEMIC
15 School doctor’s a fool (5)
Sch (School) + MO (Doctor) = SCHMO
16 Painting is unfinished! Good base for tax for upkeep of wall? (6)
Mural – l (unfinished) + g (Good)N + E (base as in logs) = MURAGE
20 Pillowcases hide most of the old deep collars (7)
Beres (pillowcases) around (hide) Th (most of the) = BERTHES
21 Open boat, crewed by women, starts to upset men in Alaska (5)
U + M (Starts of upset men) + I + Ak (Alaska) = UMIAK
22 In Cornwall throws cast out on top of surf (5)
(cast)* [Indicated by out] + s (top of surf) = SCATS
27 Japanese plant name is “noodles” (5)
Udo (Japanese plan) + n (name) + s (is) = UDONS (Japanese too)
30 Less strict? Run in old companion (5)
Feer (old companion) around (indicated by in) r (run) = FREER
31 Beginning to develop northern route for climbers (7)
N (Northern) + ascent (route for climbers) = NASCENT
33 Perhaps rode, in a windstorm, lacking a certain education (6)
Cyclone – one (windstorm lacking a certain) + Ed (Education) = CYCLED
34 Shoots around American highways (5)
Rods (shoots) around a (American) = ROADS
36 Miss Turner eats Indian spinach and pasta (7)
Lana (As in Lana Turner) around (indicated by eats) Sag (Indian Spinach) = LASAGNA
39 Following a squall on the Clyde navy submerge (5)
Drow (Scottish for squall) + N (Navy) = DROWN
42 Lofted hits Sykes played round end of over (6)
(skyes)* [Indicated by played) around r (end of over) = SKYERS (as in Cricket)
43 Inconsistent investing a large sum of money in a place of debauchery! (6)
Pot (large sum of money) in (investing) Sty (Place of debauchery)
DOWN
1 American journalist drank regularly (4)
Us (American) + Ed (journalist) = USED
2 Caber tossed round Channel Islands fragmented rock (7)
(Caber)* [indicated by tossed] around CI (Channel Islands) = BRECCIA
3 Notice after chest fails X?ray unit (3)
Remark (Notice) – Ark (Chest) = REM
4 Flash on and off when engineers’ body holds back abrasive carbon (6)
Se (Engineers) around Rev(Bort) (Abrasive carbon) = STROBE
6 Scoundrels follow on repeats (6)
Curs (Scoundrels) follow Re (On) = RECURS
7 Old right to cut green trees is evident (5)
Mmm O (Old) + Vert (Green trees) {Not sure what purpose right has in this clue} = OVERT
8 Extremely admirable person is an old man of good birth; not half … (3)
Gemman (Old word for gentleman) – half = GEM
9 … a sublime man, a liberal indeed (3)
A + L (Liberal) + I (indeed) = ALI (as in the boxer)
10 Maybe Texan never holds more than allowed without wanting money (9)
Nary (US word for never) around (indicated by holds) Excess (More than allowed) – x (without) = NECESSARY
13 A tailless donkey in a frenzy (4)
A + Moke (Donkey) – e = AMOK
15 Uncertain time hence in Scottish island’s middle (7)
Med (Middle) in Soay (Scottish Island) = SOMEDAY
16 Soldier hired foreign car (4)
DD = MERC (Mercenary and Mercedes)
17 Evacuates German — and French abruptly see off (7)
G (German) + Et (and in French) + Tersely (Abruptly) – ely (see) = GETTERS
18 Relative wearing thick coats boils (9)
Uncle( relative) in Furs (Thick coats) = FURUNCLES
19 Sailor by northern lake (4)
Tar (Sailor) + N (Northern) = TARN
23 A little Scottish conservative sits on ballot box! (4)
C (Conservative) + Urn (Ballot box) = CURN
25 Smooth Scotsman lacks yen (4)
Sandy (Scottish Name) – Y (Yen) = SAND
26 Our date fixed to retrieve data (7, 2 words)
(Our date)* [Indicated by fixed] = READ OUT
28 American poet’s prophet embracing Greek goddess (6)
Seer (prophet) around Ge (Greek Goddess) = SEEGER (As in Alan Seeger a US poet who was murdered in the first world war))
29 Various males round up last of regular wanderers in the countryside (6)
Stags (Males) round R (last of regular) = STRAGS
30 American agent seizes old land held conditionally (4)
Fed (American agent) around O (Old) = FEOD
32 Ancestrally linked, organisms covered earth (5)
Clad (Covered) + E (Earth) = CLADE
35 Race in outskirts of Daventry (4)
In + Dy (Outskirts of Daventry) = INDY
37 Bird, found in America and the United Kingdom (3)
A (America) + Uk = AUK
38 Long to ditch film-maker in channel off the St Lawrence? (3)
I assume a word for long removing a film director but can’t see it = SNY
40 Limited space for short marsupial (3)
Room – m = ROO
I think it might be DIE out of DISNEY.