Across:
1 Pressure (STRESS) to test the heart rate (STRESS test),
4 Completely clean (SPOTLESS) of drugs (-POT-) after (= position indicator) first sentence (first ‘Sentence’ = S-) for smaller amount (-LESS) (SPOTLESS),
9 Shady type (COLOUR) opens 14 across (opens ‘colour scheme’ = COLOUR),
10 Adam leaves chambermaids (‘Adam’ leaves ‘chambermaids’ = chmberis = BESMIRCH) to drag through the mud (BESMIRCH),
12 Awful (= anagram indicator) miser (miser = IM-ERS) welcomes blog entry (-POST-) (IMPOSTERS) by The Pretenders (IMPOSTERS),
13 Stand in (LOCUM) line (L-) with officer (Officer Commanding = -OC-) expressing hesitation (-UM) (LOCUM),
14 Some of The Reds (colours = COLOUR S-) with revolutionary (-CHE-) could be fairly (half of) mean (half of ‘MEan’ = -ME) (COLOUR SCHEME) and capable of lowering the tone in The House (COLOUR SCHEME),
18 A foreign (a = UN-) kind (-CHARITABLE) (UNCHARITABLE) or type that’s inconsiderate (UNCHARITABLE),
21 Pull (CLOUT) copyright (C-) for Yahoo (yahoo/thug = -LOUT) (CLOUT),
22 What someone with a growing concern presumably requires (SEED MONEY for growing/gardening) for financing start-up (SEED MONEY),
24 Board members (CHAIRMEN) from Switzerland (CH-) join those on the plane (-AIRMEN) (CHAIRMEN),
25 Ruffle someone’s feathers (ENRAGE) with a Green (a green = ENRAGE) remedy (= anagram indicator),
26 Passed (EXCELLED) divorcee (EX-) on the phone from New York (-CELL- phone) to editor (-ED) (EXCELLED),
27 Poor (= anagram indicator) Dante (Dante = DENTA-) finds fifth circle (fifth ‘circLe’ = -L) (DENTAL) is like pulling teeth (DENTAL).
Down:
1 Break the law (sin = S-IN-) around college? (University College Cork = -UCC-) Go to court (-CT) (SUCCINCT) with brief! (SUCCINCT),
2 Stout (ROLY-POLY) brewed (= anagram indicator) poorly (poorly = ROLY-PO-) at heartless (a) place (‘lay’ without ‘a’ = -LY) (ROLY-POLY),
3 Knocks (STUNS) aioli from Saint Louis (‘aioli’ from ‘Saint Louis’ = sntus = STUNS),
5 Seek justice perhaps (PRESS CHARGES) for Pulp (PRESS), Rush (CHARGE-) and One Direction (South = -S) (PRESS CHARGES),
6 Release (emit) revolutionary (= reversal indicator) (emit = TIME) with cap (LIMIT) (TIME LIMIT) by deadline (TIME LIMIT),
7 Improve (ENRICH) tea from Catherine (‘tea’ from ‘Catherine’ = chrine = ENRICH),
8 Type of business (‘Small to Medium-sized Enterprise’ = SME = S-ME) entertaining revolutionary (-CHE-) (SCHEME) plan (SCHEME),
11 Works in the abbey (works in The Abbey Theatre = SETS THE SCENE)? That explains everything! (SETS THE SCENE),
15 Strange (UNNATURAL) organisation (UN-) is unaffected (-NATURAL) (UNNATURAL),
16 Worker (A-NT) admits holding burger (-BUN- holds burger) for relative (-DA-) (ABUNDANT) – that’s rich (ABUNDANT),
17 Father (Rev = VER-) retires (= reverse indicator) at the end of January (end of ‘JanuarY’ = -Y) approaching spring? (WELL) (VERY WELL) If you say so! (VERY WELL),
19 DNA removed from Icelandic (‘DNA’ removed from ‘Icelandic’ = icelic = ICICLE) spike that’s frozen (ICICLE),
20 Going all the way back (= reversal indicator), agency (CIA = -AIC) opens with same old mistakes (opens with ‘Same Old Mistakes’ = som = MOS-) (MOSAIC) – therein lies the pattern (MOSAIC),
23 Cut into small slices (MINCE) side of Neufchâtel (side of ‘Neufchâtel’ = -N-) welcomed by cheese lovers (mice = MI-CE) (MINCE).