9  Before headmaster's back, trace the potentially disruptive pupil (9)

10 Having nothing special, Barking looking rough reportedly (5)

11 Disperse the rioters, arresting a number (5)

12 Controversial Swiss organisation nearly attracts recently disheartened VIP (9)

13 One's pressed to provide room with alternative functions next door? (5,3)

15 Clever book title (6)

18 Bill's daughter, out for run, getting severe reprimand (6)

19 Napoleon, typically bit that isn't covered during my exam (8)

22 Wrong dish I start to eat at lunch (9)

24 State deducting money from German parent (5)

26 Diamond, possibly ace, being turned over is strange (5)

27 Supermarket notice to customers exhibiting unacceptable behaviour? (3,2,4)

28 Wooden clubs at top golf course? Crazy! (4,2,3,6)

 1  Pitches product ultimately that's accepted by DIY chain (7)

 2  Group of three, extremely loathsome when arriving at hotel (5)

 3  Step in at home and organise event, consuming beer occasionally (9)

 4  Highest point in Greenwich, it boasts prime property (8)

 5  Search lasting an awfully long period (6)

 6  Teacher's pet has time off (5)

 7  Wistful from losing cat unexpectedly (9)

 8  Scramble in vault to find space up above (7)

14 "Rubbish", claims the one seeking secret of eternal youth (9)

16 In May's Government, did it involve herself replaced, posh fellow coming in? (9)

17 Game permit collected by road (8)

18 In conversation regret unkind remark, it's nonsense (7)

20 Type of school, place encouraging growth with well-rooted discipline? (7)

21 Address of firm located within current street (6)

23 Tongue, intrinsic to dolphin digestion (5)

25 Hurry to join tail initially following criminal (5)