Across:
1 Mark (SIGN-) English (-E-) takes time (-T) (SIGNET) in Ring (SIGNET ring),
4 Graduate (BA = AB-) reflects (= reversal indicator) on topless (c) bathing area (‘cove’ without ‘c’ = -OVE) for everyone (ALL) (ABOVE ALL) in a heavenly location (ABOVE ALL),
9 Colourful types (AMBERS) perhaps – they remind drivers of Should I Stay or Should I Go? (traffic lights/warning lights = AMBERS),
10 Manage (ENGINEER) Mastermind? (ENGINEER),
12 Get in the way of (INTERFERE) writing (from the 3Rs = -R-) Tenerife (Tenerife = INTE-FERE) novel (= anagram indicator) outside (INTERFERE),
13 It’ll come out (EXUDE), old partner (EX-) is due (due = -UDE) treatment (= anagram indicator) (EXUDE),
14 Swingers (MIXED DOUBLES) involved in court proceedings? (MIXED DOUBLES on tennis courts),
18 Leaves (“deserts” = “desserts” = DESSERTS-) report (= homophone indicator) on (-ON) last (= position indicator) cruise ship (P&O cruise ship = -PO-) (DESSERTSPOON) – of course, it goes down sweetly with mouthy type (DESSERTSPOON),
21 Unfinished (e) Dublin hospital (Coombe Hospital, Dublin) (‘Coombe’ without ‘e’ = COOMB) in The Hollow at Hillside (COOMB),
22 It’s about (RE-) model (-EXHIBIT) (RE-EXHIBIT) put out by the curators again (RE-EXHIBIT),
24 10,9,8,7,6,5,4,3,2,1 (numbers go from ‘10’ to ‘1’ = TEN TO ONE) =1,250? (12.50pm = TEN TO ONE),
25 Give out (ASSIGN) to fool (ASS-) upsetting soldier (GI = -IG-) in the middle of panic (centre of ‘panic’ = -N) (ASSIGN),
26 For example in 24 across, if it’s going to win (for example, “ten to one”, if it’s going to win = A GOOD BET), it’s worth backing (A GOOD BET),
27 Strong point (TALENT) in story (TALE-) from religious books (New Testament = -NT) (TALENT).
Down:
1 Grounds (STADIUMS) for all the characters upsetting (= reverse all indicator) development authority (IDA= -ADI-) consumed by lewd material (smut = T-UMS) that’s endless (end ‘less’ = S-) (STADIUMS),
2 Pay for taking journey (GO BY TAXI) over (= reversal indicator) marsh (bog = GO B-) to yard (-Y) outside airport (TAXI) (GO BY TAXI),
3 It’s a mistake (ERROR) heading off (t) with local rascal (‘terror’ without ‘t’ = ERROR),
5 Rolls (BUNS-) off half the oxen (off half the “oxen” = -EN) on Burren (Burren = BURNER) reproducing (= anagram indicator) (BUNSEN BURNER) part of a classy scientific experiment to generate a bit of heat (BUNSEN BURNER),
6 Express (VOICE-) Takeaway (take away = -LESS) (VOICELESS) for Mum perhaps? (keep mum/quiet = VOICELESS),
7 A (A-) scene (-VENUE) (AVENUE) out of The Road (AVENUE),
8 Fat (LARD-) engineer (-E-) by mid-afternoon (mid ‘afternoon’ = -R) (LARDER) is storing a supply of food (LARDER),
11 Forceful reproachful protest (REMONSTRANCE) is about (RE-) brother (monk) briefly (k) (‘monk’ briefly = -MON-) taking position (-ST-ANCE) over writing (from the 3Rs = -R-) (REMONSTRANCE),
15 What the count is supposed to have done (Count Dracula DREW BLOOD), Picasso did it in his painting of Guernica (DREW BLOOD),
16 Device (BOMB) for the builders (SITE) (BOMB SITE) is blown out of all proportion (BOMB SITE),
17 Has natural ability (INSTINCT) to nose? (INSTINCT),
19 Local diamonds (local “diamonds” = ICE) sourced from China originally (TEA) (ICE TEA) by cool type during the summer (ICE TEA),
20 Delivered (BORN-) last (= positional indicator) order (-O) by middle of September (middle of ‘September’ = -E-) (BORNEO) to a primitive lad’s home perhaps (BORNEO),
23 Head of state dismisses defeat (‘head of state’ dismisses ‘defeat’ = haost = HOSTA) in the plot (HOSTA).