'Playfair' by Jock McScrabbet

In a ‘Playfair’ code-square, letters of keyword, in which no letter recurs precede the rest of the alphabet in order. ‘I’ does duty for ‘I’ and ‘J’.
Answers to 4 clues with asterisks are to appear in the diagram in code according to a code-square with a key-word which has to be discovered.



Across
*1  A clue by Ximenes? Restore me with a gin (6)
5   A perch by a hilltop – so. It’s called climbing (6)
9   Seaweed in morning tea. Get knotted! (10)
10 Retiring, blushing – that’s the bird for bed-time warmth (5)
11 Georgian piece of silver, Regency and British to the core (5)
13 Beloved region, no longer cultivated (8)
15 Worries lightly touched on by the Beatles (5)
16 Extremes of eloquence about a lifeless person (5)
17 In the vernacular has no ma – defective like (7)
19 Absent-minded fellow – one always going about undressed (7)
21 Those who don’t get HCs go about inward wrecks (5)
23 A little book-learning is a dangerous flaw (5)
26 I’m often found in bed making lechers come to grief (8)
27 Summer month and hints of holiday time: is there _____better? (5)
28 Feature of a pillar, rising between flutes (5)
29 A daftie, a daftie – chewed gum not for chewing (10)
30 County – when one is genteel, to make things plain (6)
*31 X in the Indian post: his letters often are (4)
 Down
1  This was evidence when Adam was a bachelor (6)
2  To be blunt indeed, a sickening uppish way of speaking (10)
3  Pappy, dear pappy, will make me a train (6)
4  High flier in the US Intelligence reveals a border plant (7)
5  One has to be in step to one-step (5)
6  Being of substance, tawny, attractive am sexy (not half) in a bus (8)
7 Old measure – one that varies, rising in pace (6)
*8 Heavy stuff? It’s got arty BA puzzled (6)
9  A divine abbreviated wisp of skirt brings out the total figure (4)
12 Anagram from X – using it he produces the reverse of light (10)
14 Jelly – taking fish after one, it’s bound to repeat (8)
18 Deadly, hearless vile – could describe the Romanovs (7)
*19 Short down clue about nothing – for a silly ass (6)
20 Sturdy old Wellington in decay (6)
21 What shopkeepers do about a queue. Tell the others? (6)
22 One finds endless children saying this is fun (6)
24 An object of respect until balance on its head (5)
25 Jock’s unmatched and Pat’s by Jove, unbegged (4)

Note for detectives - who is Jock McScrabbet?

One of  Eric Chalkley's early puzzles, Ximenes commented on all the clues. In answer to the question, X wrote -
Presumably E. C. , but Poirot alone knows why! Please explain. Very good fun. I thoroughly enjoyed it and took longer than I usually do in finding the key-word. I've had a fair amount of practice at it through getting someone to set me the equations to work from (without a crossword). At least 6 really excellent clues, but a few criticisms too, I'm afraid.  Many thanks, X.