Cryptic crossword

Friday's puzzle...

ACROSS

1 It's cheap to enter an air space with gravity (5,3,1,4)

10 You can travel via places like Helsinki, Hamburg and Hobart with these (9)

11 In wartime, German will be adopting Scottish expression (5)

12 Be sick about Open University's makeover (7)

13 Gathered into the middle but said to be spoilt (7)

14 All by the sea in France for June, July and August (6)

16 Method artist used to tell musician to take it easy (8)

18 Gain dues, possibly, through prayer (5,3)

20 First couple of speakers phoned and pounced (6)

23 That woman may knock situation(7)

24 Drop hat in conversion of non-convertible (7)

26 Presses for severe restraints (5)

27 Hear Tom and me suffered foot deformity (6,3)

28 Having an honest victory at country gathering with urban setting (4,3,6)

DOWN

2 Ready to be shot, perhaps, at start (5)

3 Came back to write music for one of "The Planets" (7)

4 Darcy's alter ego's seen in Moray and Cromarty (6)

5 Belgravian downstairs maid would be said to have material suitable for cabinets (8)

6 It's out of this world, what's found under field dressing (7)

7 In Northern Ireland bed, Scotsman put a tobacco plant (9)

8 Be one of the crew on sailing and cruising activities, for example, showing appreciation of fair play (13)

9 Be on top and yearn to sink in ocean very fast (8,5)

15 State of chaos - it's an omen! (9)

17 Wander glen, then stretch out (8)

19 Study grammar in extreme stupor and it becomes more hard to get (7)

21 Upstart to 'ave prune put in stew (7)

22 Charles places member among the winners (6)

25 Goodbye to original real Turk (5)