Across:
1 Cost (PRI-CE) includes mean (median/mid point) lunch (mid point of ‘lunch’ = -N-) (PRINCE) for regular at The Palace (PRINCE),
4 Commercial vehicle (STAFF CAR) for major employer (STAFF CAR for major employer/ army),
9 Guidelines (ADVICE) for Bill (AD-) with bad habit (-VICE) (ADVICE),
10 Spheroid (BALL-) from space (-ROOM) (BALLROOM) is synonymous with old romance (BALLROOM of Romance),
12 I’ve no idea (DON’T ASK ME) mafia boss (DON-) is some piece of work (task = -T ASK) and fairly (half of) mean (half of ‘mean’ = ME) (DON’T ASK ME),
13 General type of direction for those in charge of War Horse, presumably (ORDER from army general), in The Abbey (ORDER),
14 Most of those in 7 down (most of ‘crowds’ = CROWD-) and 20 down (‘please’ = -PLEASE-) writing (from the 3Rs = -R) (CROWD-PLEASER) popular form of entertainment (CROWD-PLEASER),
18 The arts (CULTURE) student’s first (‘students’ first = S-) job in the pawnshop (-HOCK) (CULTURE SHOCK) comes as a surprise to The Tourists (CULTURE SHOCK),
21 Talk off the cuff (AD LIB) for ages leaving bag ladies (‘ages’ leaving ‘bag ladies’ = bladi = AD LIB),
22 It’s as close to the end as you could possibly get (NEAR FATAL) and within walking distance of (NEAR -) a flat? (a flat = FATAL) Bizarre! (= anagram indicator) (NEAR FATAL),
24 Board member (CHAIRMAN) from Switzerland (CH-) is on the plane (-AIRMAN) (CHAIRMAN),
25 Stand up to (RESIST) bank’s research scientist (bank’s ‘research scientist’ = RESIST),
26 Compliance (MEEKNESS) of nemeses (nemeses = MEE-NESS) working (= anagram indicator) over the weekend (‘week’ end = -K-) (MEEKNESS),
27 Handpicked (CHOSEN) by Charlie (C-) Pipe (-HOSE-) to condemn foundation (‘condemn’ foundation = -N) (CHOSEN).
Down:
1 Gamble (PLAY DICE) could be a drama (PLAY) for Las Vegas rollers (DICE) (PLAY DICE),
2 Drunk (= anagram indicator) vintner (vintner = INVENT-R) swallows nothing (-O-) (INVENTOR) produced by pioneer? (INVENTOR),
3 Has no input in occupation (has no ‘input’ in ‘occupation’ = occao = COCOA) producing hot drink (COCOA),
5 Tenor (T-), old French composer (Maurice Ravel = -RAVEL) and sailor (able-bodied seaman = AB-) take to the road (-ROAD) (TRAVEL ABROAD) and go overseas (TRAVEL ABROAD),
6 The supporters of team (FOLLOWERS) tour (= anagram indicator) of Roswell (of Roswell = FOLLOWERS),
7 Types of masses (CROWDS) for a number of flocks (CROWDS),
8 State (REMARK) shirt-maker hits out (‘shirt-maker’ hits out/without ‘hits’ = rmaker = REMARK),
11 They unlock many doors (SKELETON KEYS) in the museum (SKELETON) for openers? (KEYS) (SKELETON KEYS),
15 Taken by patient (DRUG), captain of industry (BARON) (DRUG BARON) and speed-merchant? (DRUG BARON),
16 Keeps under control (CONTAINS) with messy (= anagram indicator) sanction (sanction = CONTAINS),
17 Stripped of meat (SKELETON) and fresh (= anagram indicator) leeks (leeks = SKELE-) and it’s not (not = -TON) served up (= reversal indicator) (SKELETON),
19 Gangster (-AL- Capone) followed by copper (-CU-) consumed by thulium (T-M) (TALCUM) – a white powdery substance (TALCUM powder),
20 Polite request (PLEASE) for parking (P-) to rent (-LEASE) (PLEASE),
23 Riot comes out of rifle shot (‘riot’ comes out of ‘rifle shot’ = flesh = FLESH) – those in 17 down won’t get this (‘skeleton’ won’t get FLESH).