Fifteensquared

Not a lot to say about this one.  Some familiar words and nothing which needed a great deal of explanation.
8A was not entirely clear to me, but seemed the likely answer. 

ACROSS

1.    INTACT – ( hidden: JOint actUALLY)
4.    MATTRESS – (* starts me)
9.    SORDID – ( s-or-did )
10.  ANGELICA – ( angelic -a : stems of the plant are often crystallised and used to decorate cakes.)
11.  ARABLE – (arab-leA)
12.  BLACKOUT – (black-out : to ‘black’ someone is to ‘ bar’ them as in black-balling)
13.  SAD – ( s-ad.)
14.  DROVER- (d-HErD-over)
17.  RANSOME – ( ran-some.  Arthur Ransome [1884-1967], author of Swallows and Amazons inter alia.)
21   PUTTER – (p-utter – a golf club)
25.  LOG – ( dd)
26.   BENJAMIN – ( *menjab in)
27.  TOPPER – ( top-p-er)
28.  INIQUITY -(i-n-i-quit-y)
29.  TENNIS – ( <sin net)
30.  THE BLUES – ( ‘lu’ within Thebes – a city we met recently in another puzzle)
31.  ANCHOR. – (an-chorE – an anchor man is a presenter on TV)

DOWN

1,2.  IT STANDS TO REASON – (it (Italian)-stands to reason, as a barrister does in court)
3.    CHILLIER – ( c-hillier – Tristram Hillier ( 1905-1983.  English Surrealist artist)
5.    ARNOLD – ( * Roland.  Matthew Arnold (1822 -1888) English poet, mainly remembered by me as writer
                           of the’ Forsaken Merman’ which impressed me greatly as a child)
6.    TRENCH  – ( t-r-ench. Presumably the ‘ r ‘ is for rook, AKA castle, in Chess)
7.    EDISON – (e-d-is-on – Thomas Edison, inventor of the light bulb and phonograph)
8.    SPARTA – (s-part-a – not certain about the SA)
12.  BASSOON -  (bas-soon)
15.  RAP – (rapT)
16.  IMP- (i-mp : he occupies a seat in Parliament)
18.  EUROPEAN -( <rue-ope-a-n)
19.  AT A PINCH – ( a -tap-inch)
20.  DRY RISER -( ‘is’ within * derry BAr – a main vertical pipe for distributing water as part of fire suppression;
                                     It is maintained empty of water.)
22.  OBOIST- (*bootsi)
23.  INSIDE – (dd. the content being what is inside, and euphemism for ‘in prison’)
24.  SAMUEL – ( * us male – book of the Old Testament)
25.  LITTLE – ( litt-l-eR)