The usual excellent, accessible, entertaining, fare.
Solving time: 19 mins
* = anagram
ACROSS
1 BLOOMS BURY Not a container and contents!
6 C (A) MP
12 LIST-LESS
21 MAIN STAY Sea = main also used in Times today.
24 CAT S The musical
25 NIGHT NIGHT A contributor to this site nearly gave this away last night under “setters” “Knights” = chessmen (men on board)
28 S ARK Channel Island
21 ME THUS ELAH Hale reversed (also used in Times today)
DOWN
1 BLENCH Double definition
3 MARCH 1 (start of month) ONE SS
5 RUSSIANIST (is anti-USSR)* Topical
8 PARA SITE
13 THE SOPRANOS (A person shot)* &lit a watcher assures me.
14IM (o)PERATIVE Definition: required No hat = take off first letter (in a down clue)
16 HAM MOCKS
19 BEN GAL
20 STITCH Double definition
23 UH-UH Take soldiers (TA) twice out of Utah. US usage for no (had to verify that)