Times 25453 - In decline

I found it very hard to work up any momentum on this and having struggled to get started I battled through most of it at snail pace with only occasional bursts of energy to restore my flagging spirits. In the end I completed it in 58 minutes. There's nothing at all obscure here other than an unknown alternative spelling, so my problems must be down to mental powers failing towards the end of a long day.

* = anagram

Across
1	ACCOST - COS (function) inside ACT (law)
5	AS THOUGH - TOUGH* inside ASH (volcanic output). Definition: Like
9	BUTTERMERE - BUT (save), TERM (time), ERE (before). One of many lakes in Cumbria.
10	TWIG - patienT, WIG (simulated shock). My clue of the day!
11	DECEASED - CASE* inside DEED (action)
12	SUNSET - SUN (newspaper), SET (group). I lost time here with the thought that the newspaper group might be NI, and even possibly in decline.
13	ACRE - C (constant) inside AREa (most of what it measures)
15	FORSAKEN - OR (men), S (sons) inside FAKE (false), N (name)
18	MAGDALEN - DALE (valley) inside MAGNetic (half of attractive). This is the Oxford college pronounced Mawdlin as opposed to the Cambridge one that as an E on its end.
19	SMEW - Microwaved inside SEW (baste)
21	TEMPER - TEMPtER (baiter short of time). I didn’t know 'bait' as an alternative to 'bate' for bad temper.
23	SEAFARER - AFAR (at a distance) inside SEER (oracle)
25	JOIN - JOb (mostly work), IN (home)
26	CHICKEN OUT - CHIC (stylish), KEN (man), OUT (unfashionable)
27	DE GAULLE - AGED (reversed), sULLEn
28	TURTLE - TURn (brief spell), LET*
Down
2	CHUTE - I think 'fall slower' is being used as a nounal phrase  but I stand to be corrected by the grammar experts. The second part of the clue amused me because 'para' doesn't need to be dropped for it still to be a 'fall slower'.
3	ON THE MEND - O, aNTHEM (rousing song without a), END (finale)
4	THRASH - THe, RASH (headstrong)
5	AHEAD OF ONES TIME
6	TREASURY - (A RUSE)* inside TRY (bid)
7	ORTON - Hidden. Joe (actually John) the playwright (1933-1967). I wonder if 'Ortonesque' has ever appeared in the grid.
8	GUINEVERE - GUIdE (lead) with 'd' for daughters replaced by NEVER (at no time). She was King Arthur's Queen Consort.
14	CHAPERONE - H (hard), APE (beast) all inside CRONE (old woman). 'Woman' is doing double duty here as part of the wordplay and in the definition.On edit, retracted following vinyl1's comment which got me to read the clue again. Thanks, v.
16	ABSTAINER - (TEA IN BARS)*
17	CLERICAL - C (Conservative), L (left), ERICA (heath), L (Liberal). I thought old Ted was having yet another outing so I was pleased when I found I was mistaken.
20	GASKET - ASK (petition) inside GET (capture)
22	PANDA - PAN (criticise), AD (commercial, reversed). Easiest of the day, I think.
24	EQUAL - E (English), QUALm (unease shortened)