4093 Times Group by Colleague

This was a nice puzzle from Colleague. Some easy clues made for an easy grid fill. It was much more difficult to find the groups. The three Rs was formed from ARITHMETIC, WRITING & READING (*DERAIGN). The five Ks is KARA (*ARAK), KHANGA, KESH, KACCHA & KIRPAN (*PARKIN). Five times three is fifteen and we were looking for the Fifteen Os, a series of meditations by St. Bridget. Her name had to be entered in the space at the bottom of the grid and the word MEDITATION was to be highlighted, forming a circle in the centre of the grid.  The two barred-off cells were to be filled with Os to make the number of Os in the grid add up to 15.

Across
1 Old treatise on calculation produced by a scruffy hermit with a twitch (10)
ARITHMETIC A + Anagram HERMIT + TIC
8 Tree with poisonous seeds has bark removed to make strong drink (4)
ARAK (k)ARAK(a)
11 Working in papal office, he received lands from Scottish Crown (8)
DONATARY ON in DATARY
12 Leave without notice from regressive banking organisation (5)
SCAPA APACS (Association for Payment Clearing Services) reversed
14 Henry's not involved in distorting stuff put on paper (7)
WRITING WRIT(H)ING less H (Henry)
16 A biscuit chest in cut wood (6)
PARKIN ARK in PIN(e)
17 Diploma of Art being just good enough for merely painting borders on walls (7)
DADOING DA in DOING
18 Local branch of greenies regularly losing embarrassment (4)
REIS gReEnIeS
19 Lawyer active about leader of Hezbollah's arrest (6)
ATTACH ATT (Attorney) + a (active) + C (about) + H(ezbollah)
20 One gets inside quick, taking the last in for a wee snifter (7)
DRAPPIE I in DAPPER moving last letter inside
22 Banded creatures Goethe classified to some extent (6)
THECLA Hidden
24 Excellent being back in dizzy blonde's library (8)
BODLEIAN AI reversed in Anagram BLONDE
28 Lerwick's small pier damaged around 6th of October by tail end of hurricane (6)
PEERIE Anagram PIER + (octob)E(r) + (hurrican)E
30 Napoleon, perhaps, about to thump provincial Spanish military man (7)
SOLDADO DAD in SOLO (ref. Napoleon Solo, the Man from Uncle)
32 Very wicked demand (6)
DAMNED Anagram DEMAND
33 Be unsteady inside until forced back (4)
FLIT Hidden reversed
34 Baby's anticipated arrival time being put back after gas is given (7)
NEONATE ETA reversed after NEON
36 Express surprise Conservative madcap once nearly returned in short trousers (6)
KACCHA AH + C + CAK(e) all reversed
37 Old set in battle array put one in desperate danger (7)
DERAIGN I in Anagram DANGER
38 Dried pepper used in bean chowder (5)
ANCHO Hidden
39 The most irritable and fractious set in Bow Street (8)
TESTIEST Anagram SET in TIE + ST
40 American's to fix possible Oxford broadcast (4)
SHOO Homophone SHOE
41 "Praying Mantes" are rewritten by body of top Scottish scientists in Greek letters (10)
REARHORSES Anagram ARE + RSE in RHOS (Greek letters)
Down
1 16th century honours dead in battles after active duty (7)
ADWARDS AD (active duty) + D (dead) in WARS
2 New member's worried after enjoying success at beginning of inauguration (8)
INITIATE IN IT + I(nauguration) + ATE (worried)
3 Ponies with time in racecourse enclosure (5)
TATTS T in TATS (ref. Tattersall’s)
4 Local must kiss certain islanders (4)    
MANX MAN (must) + X
5 Invading metamorphosed host, this insect would have been of another kind (6)
ERGATE OTHERGATES less Anagram HOST
6 Book translator's story about Edmund's India (7)
TYNDALE YND in TALE
7 Influence of independent politician over American court (6)
IMPACT I + MP + ACT
8 Flowerless plant with mouthlike openings rising about tip of calyx low-down (7)
ACROGEN C(alyx) in ORA reversed + GEN
9 Moving eight across, drinking one, could be Bulgarian's one over the eight? (5)
RAKIA Anagram ARAK (8 across) including I
10 Piece of cotton cloth around top of head - a hair adornment (6)
KANGHA H(ead) in KANGA
13 Under pressure, Walter's friend had harassed Glaswegian (7)
PINGLED P + INGLE (ref. Sir W Scott) + ‘D
15 Breach in igloo's sides flooded forest area (5)
IGAPO GAP in I(glo)O
21 School function's not left with faculty president (7)
ROEDEAN ROLE less L + DEAN
23 Fellow trimmed variety of lisle to make soft fabrics (8)
CHALLIES CHA(p) + Anagram LISLE
24 Wild horse dragging truth finally from branch manager in the US (7)
BRONCHO (trut)H in BRONCO
25 Fifty ordinary soldiers - soldiers breaking pods (7)
LOMENTA L + O (ordinary) + MEN + TA
26 Rising urge to leave Channel Island? Fly is the answer (5)
ALDER  ALDERNEY less YEN reversed
27 Old supports set field pulpit in position (7)
POTENTS TENT in POS.
28 God follows style of rock fans (6)
PUNKAS PUNK (rock) + AS
29 Perhaps Morgan's food brought up for example at absolute end of binge (6)
EATAGE EG + AT + A (absolute) + (bing)E all reversed (Morgan is a type of horse)
30 More dishonest supporter of one particular viewpoint involving nation's leader (6)
SNIDER N(ation) in SIDER
31 Confined to camp in menagerie's plain architectural feature (5)
ZOCCO CC in ZOO
33 Sides swapped in rush for stylishness (5)
FLAIR FRAIL swapping L & R
35 King afraid for some without navy. Big shock? (4)
KESH  NESH swapping N (navy) for K