Thank you, Pedro, for this well appreciated reminder of the wit and wisdom of the great Douglas Adams and the question of Life, the Universe and, well, just Everything (5, 8, 11). Our 'star' Arthur Dent (18, 16, 19) makes his appearance (perhaps appropriately) toward the bottom end of the grid.
The number of the puzzle - 1071 - translates to 42F in hexadecimal. I’m sure HHGTTG fans will find plenty to think about in that. Actually, this is as irrelevant as what anyone had for dinner a week ago - but do enjoy whatever you do (without harming anyone else).
Improbably, all this became clear only after completing the grid which took 12 minutes and felt like I was making heavier weather of it than I should (which made me REALLY depressed - brain the size of a planet and I miss the 10 minute target). There doesn’t seem to be much which is obscure - except maybe the word play of 13dn but the definition was clear, and the clever hidden at 11ac. The experience of others would be interesting.
Cod to 8ac for first making me realise the connections.
So long and thanks (in advance) for all the comments.
ACROSS
1. Mea culpa - it’s my fault ('We apologise for the inconvenience'). Copper (CU) interrupting dinner, say (MEAL) with secretary (PA).
5. Life (don’t talk to me about it) - biography=life story/life. Story (LIE) encompassing fine (F).
8. Universe - a lot of space - 'Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space'. Place to study (UNI), poetry (VERSE).
9. Wing - faction of party. Success (WIN), (G)overnment.
11. Everything - all. In the clue (ingredients of) som(E VERY THIN G)ruel.
14. Lariat - cowboy's accessory - a rope used as a lasso or for tethering. US city (LA), lowlife (RAT) carrying one (I).
15. Newton - scientist. Fresh (NEW) measure of mass (TON). Measure of mass works for me but if there are any doubts it also means a freight ton which is often taken as 40 cubic feet, 1 cubic metre, or 1000 kilograms.
17. Popularity - mass appeal. Anagram (crazy) of PLAY I TOUR containing power (P).
20. Hoop - ring. Hard (H) work (OP) containing old (O).
21. (Agatha) Christie - crime writer. Vica(R) in church (CH), is (IS), restriction (TIE).
22. Dark - sinister. Vessel (ARK) pursuing daughter (D).
23. True Grit - John Wayne movie. Time (T), to regret (RUE), stones (GRIT).
DOWN
1. Maul - (loose) scrum. Ponder endlessly (MUL)l around a (A).
2. Arid - (a description) of desert regions. Area (A), free (RID).
3. Unenviable - in no way admired. Anagram (working) of IN LAB VENUE.
4. Pastry - some baking. Father's (PAS), attempt (TRY).
6. Initiate - make a start on. One (I), idiot (NIT), I (I), took in (ATE).
7. Engaging - double definition.
10. Streetwise - in tune with the city. Is (IS) surrounded by an anagram (various) of TWEETERS.
12. Slipshod - taking little care. Quietly hands over (SLIPS), brick carrier (HOD).
13. Trap-door - area of stage. Elevated (upwards) of cross (ROOD - a crucifix, esp one set on a beam or screen at the entrance to the chancel of a church) and section (PART).
16. (King) Arthur - regal figure. Craft (ART), almost injured (HUR)t.
18. Star - big name (in the movies). Debut cut short (STAR)t.
19. Dent - evidence of collision. (D)riv(E), (N)o(T) - both disheartened.