Across
1 Anagram (working) of “amused” = Medusa (who could turn you to stone)
4 Content (satisfied) with MP (politician) replacing N (new) = contempt = mockery
9 Larking (playing) less G (good) = Larkin, a poet
10 Scan (check) + tier (level) = scantier = not so full
12 Stale (dated as in old fashoined) + china (slang for mate) = stalemate = impossible to move in chess
13 CIA (spies) capturing EL (the in Spanish) = Celia
14 Invention (lie) around ter (term less M) = intervention = mediation
18 Anagram (revolutionary) of “shall draw in a” = Hadrian’s Wall = an old structure
21 First letter (starts) of Running Out Of Money Yet = Roomy = plenty to spare
22 Chic (smart) + a + Goan (someone from southern India) = Chicagoan
24 Anagram (abandoned) of “road we’ve” = overawed = scared
25 Violent (wild) - N (nitrogen) = Violet = a plant
26 If hard bit’s over, the rest is easy; rest easy = relax
27 Anagram (at sea) of “lose” in NN (middle letters of chaNNEL) = “Nelson”
Down
1 Mole (spy) + kin (family) = moleskin; material and a type of notebook
2 Darts (moves quickly) taking (capture) ark (shelter) = dark arts = magic
3 Spine (courage) becomes snipe (criticise) as p (president) moves down (falls in a down clue)
5 Anagram (terrible) of “practice throw” less W (weight) = orchestra pit = where band is located
6 The solution to ten across = scantier (more revealing)
7 I inside (wearing) manly (adventurous) = mainly = in general
8 Tar (sailor) + tan (sun damage) = tartan, a material
11 Safe (inoffensive) + crackers (christmas items) = safecrackers = thieves
15 Ready (money) + made (earned) = readymade, a controversial type of art
16 Anagram (troubled) of “lad comes” = Damocles” who had a sword hanging over him
17 Plank (board) + ton (not reversed) = plankton = sea food
19 Ardour (passion) sounds like (expressing) harder = how you must try to imrove
20 Popular belief of what Germans use to reserve sunbeds etc. on holiday
23 A bride (new wife) - R (resistance) = abide = tolerate