A pleasant solve from Doc, with a few obscure words that needed research …The instructions read: the unclued lights (five of two words, three singletons and a pair) are of a kind. And indeed they are all Grand Prix racing drivers, current or from the past – hence the title – F1 – Formula One. Not a subject I am very familiar with so I had to seek internet help for at least three names.
The unclued lights, and their F1 careers, are: Across:
4 JACK BRABHAM 1955-1970
12 (Niki) LAUDA 1971-79, 1982-85
23 (Fernando) ALONSO 2001-present
40 KEKE ROSBERG 1978-86
43 AYRTON SENNA 1984 – tragic death on the track in 1994. See Asif Kapadia’s fine film
Down:
3 LANDO NORRIS 2019 – present
7 (Jenson) BUTTON 2000-17
15 DAMON + 39a HILL (son of Graham) 1992-99
16 JOCHEN RINDT 1964 – 70 (also died on the track)
Across
11 Carpet from Moor includes touch of red, then russet, umber and green (9)
HEARTHRUG
HEATH (moor) around (includes) R (a touch of red) + (a touch of) Russet, Umber and Green
13 Portly chap!? (5,6)
STOUT FELLOW
Cryptic definition, stout meaning portly and resolute or unyielding
14 Season limited, it has to be said (4)
TIDE
Homonym of TIED (limited). Definition: as in there is a tide in the affairs of men
15 Rehab symptom of drunkards, topers and sots, to start with (3)
DTS
First letters (to start with) of Drunkards, Topers and Sots: def – delirium tremens
18 Foreign curios having energy – a toxic mix (7)
EXOTICA
Anagram (mix) of E (energy) + A TOXIC
19 Win majority for Brexit result, apparently? (7)
OUTVOTE
Brexit majority = voting for “out”
22 Thanks to Pierre, a kingdom of central England (6)
MERCIA
MERCI (thanks in French – to Pierre) + A
24 Bounder in a pair of spectacles for online grocery (5)
OCADO
CAD (bounder) inside O and O – a pair of spectacles
27 Indecisive English poet swaps his opposites (3-2)
YES-NO
(Alfred) Noyes – English poet – with NO and YES (opposites) swapped
29 The gift of story books (6)
TALENT
TALE (story) + NT (New Testament – books)
31 Values some customer, it seems (6)
MERITS
Hidden (some) in custoMER IT Seems
34 Alarm one tiger, first, in a barrier (7)
AGITATE
I (one) + T (tiger, first) in A DAM (a barrier)
35 Iron Maiden’s hats (7)
FEDORAS
FE (iron) + DORA’S (maiden’s)
38 Bit of sunshine right before a day’s end (3)
RAY
R (right) + (before) A daY’s last letter (end)
41 Primate some find ridiculous (5)
INDRI
Hidden (some) in fIND RIdiculous
42 You once and we and Lloyd reproduced weld (6,3)
YELLOW DYE
YE (you once) + anagram (reproduced of WE and LLOYD. Definition: weld is a yellow dye
Down
1 US poet Walt embraces PM presenter Davis and delivery driver (5,3,3)
WHITE VAN MAN
(Walt) WHITMAN (US poet) around (embraces) EVAN (Davies – presenter of PM on Radio 4)
2 New musical version, note, accepted by timeless band (5)
REMIX
MI (note) inside (accepted by) REX – T REX without the T (timeless)
5 Some of the regatta in Solent reaches (7)
ATTAINS
Hidden (some of) in regATTA IN Solent
6 The option of a Walls, say, without cherry topping (6)
CHOICE
CHOC-ICE (a Walls, say) without C (topping – first letter – of Cherry)
8 Warned of smashed treadle (7)
ALERTED
Anagram (smashed) of TREADLE
9 Ointment some cannibal mixed (4)
BALM
Hidden (some) in canniBAL Mixed
10 Take-overs of present-day 6s (9)
ADOPTIONS
AD (present-day) + OPTIONS (6d: CHOICEs)
17 Beast’s loved one strips, turning to bed early for this (6,5)
BEAUTY SLEEP
BEAUTY (loved by The Beast) + SLEEP (PEELS – strips, reversed – turning)
20 US river bird in galley gets cooked (9)
ALLEGHENY
HEN (bird) in ALLEGY – anagram (gets cooked) of GALLEY
21 Some tannoy with parts missing regularly (3)
ANY
tAnNoY – TANNOY with parts missing regularly
25 Snug modest housing for married female (5)
COMFY
COY (modest) around (housing) M 9married + F (female)
26 It’s not odd for Gollum to reveal a blind salamander (3)
OLM
Even letters (it’s not odd) of gOlLuM
28 Aggregate fruit eater chewed with joyous shout (7)
ETAERIO
Anagram (chewed) of EATER + IO (joyous shout). Definition: an aggregate fruit such as raspberries – a word I had to deduce from the crossers with some difficulty and then look up
30 Joiner by press bar (7)
ANDIRON
AND (joiner) + IRON (press)
32 Sends up drinks to card-playing opponents (6)
TEASES
TEAS (drinks) + E (East) + S (South) – opposites at Bridge
33 In Germany, sail south east around glen (6)
SEGELN
SE (south-east) + GELN – anagram (round) of GLEN. A word not in my Chambers but I suppose adequately clued
36 Lady Gaga admits bit of knitwear is polyester (5)
ALKYD
Anagram (Gaga) of lady + K (a bit of knitwear). Definition: a resin used in paints
37 Cheeky caress embracing redhead (4)
PERT
PET (caress) around (embracing) R (first letter or head of Redhead

Fun puzzle, thanks to Doc. Like Prospero I was no expert in the subject matter, but I don’t mind that in a puzzle.
Being a little pedantic, I noted that four separate clues (31a, 42a, 5d, 9d) use “some” as a hidden indicator. This felt like three uses too many.
In 6d it was pointed out to me (by another self-confessed pedant) that the ice cream maker “Wall’s” always has an apostrophe.
As for SEGELN, if you look under the entry for SAIL in Chambers, the German word SEGEL is shown as the root word where it describes ‘origin’, which is close enough, perhaps.
Thanks to Doc and to Prospero for the blog.
As a fairly keen follower of F1 this came pretty smoothly for me – just had to check the spelling of JOCHEN RINDT, and KEKE ROSBERG held out the longest. I didn’t help myself by putting in LANDO at the top right, expecting to find NORRIS elsewhere, until I found him in his entirety!
One further nuance, I think, is that they have also all been F1 CHAMPIONS in their time, right up to last year’s LANDO NORRIS…
Thanks to Doc and prospero…