Across
Looking after Barnet Hospital, show anxiety (8)
Ferret and small marsupial let out to lunch (6)
I haven't cracked this one yet — but Fifteensquared have:
definition: to rootle is to rummage around or "Ferret" ROO (short for kangaroo, "small marsupial") + anagram of (let)* anagram indicator is "out to lunch", slang for 'slightly crazy'
If so, loser becomes poser, in a manner of speaking (4)
I haven't cracked this one yet — but Fifteensquared have:
L -oser becomes P -oser, if L IS P
Thus entering wood, Picaroon moving clumsily (10)
English firm receiving tax returns in standard interval (6)
I haven't cracked this one yet — but Fifteensquared have:
E (English) + CO (company, "firm"), both around VAT (value added tax); and all reverse/"returns"
Travelling Martian bearing right in vessel (8)
I haven't cracked this one yet — but Fifteensquared have:
anagram/"Travelling" of (Martian)*, around R (right)
Pair of old ladies maintaining this compiler stinks! (7)
I haven't cracked this one yet — but Fifteensquared have:
definition: "stinks" as a plural, more than one thing that stinks a pair of MAS="old ladies", around I="this compiler"
When spotted, thong is tight (2,5)
Roundabout in Rome's outskirts? Charge around it (8)
Argos supply entertaining new donatable items (6)
I haven't cracked this one yet — but Fifteensquared have:
anagram of (Argos)*, around N (new) "supply" as anagram indicator as in 'supple'
All those present when the news is broadcast party (10)
2d
Daughter's scrubbed wild bird's cage? (4)
I haven't cracked this one yet — but Fifteensquared have:
anagram/"wild" of (bird's)*, with the d for "Daughter" removed/scrubbed
Disreputable, heartless lowlife admitting this is agony (6)
I haven't cracked this one yet — but Fifteensquared have:
L-owlif-E heartless without its inside letters; around OUCH="this is agony"
Wrongly label item, with list in shambles (8)
I haven't cracked this one yet — but Fifteensquared have:
anagram/"in shambles" of (item list)*
Down
Street musician's song from West Side Story character (8)
See 24
Don't pass on coat of lace fabric that's ribbed (6)
I haven't cracked this one yet — but Fifteensquared have:
definition: a type of cloth fabric that is ribbed FAIL="Don't pass" + outer letters (coat) of L-ac-E
Spy that thing in rotten tree? You might spy this thing in rotten tree (7)
I haven't cracked this one yet — but Fifteensquared have:
M=codename of a "Spy" in James Bond [wiki] + IT="that thing;" all inside anagram/"rotten" of (tree)*
Supplier of beef and chips popular around America (8)
I haven't cracked this one yet — but Fifteensquared have:
definition: a breed of cow i.e. a source of beef FRIES="chips" + IN="popular" around A (America)
Patient guy's making a career in work practice (shown in pairs of across answers here) (3-7)
I haven't cracked this one yet — but Fifteensquared have:
JOB'S="Patient guy's" + HARING=speeding around=careering="making a career" Job was tested by God in the Bible [wiki]
Engineering manual for student once (6)
I haven't cracked this one yet — but Fifteensquared have:
anagram/"Engineering" of (manual)*
Laying off flipping idiot involved in non-23 (10)
I haven't cracked this one yet — but Fifteensquared have:
for definition e.g. 'to lay off the sauce' meaning to give up drinking reversal/"flipping" of NIT="idiot"; inside ABSENCE=non- ATTENDANCE (using solution to 23ac)
A dieter regularly visiting capital city up north (8)
I haven't cracked this one yet — but Fifteensquared have:
A (from surface); plus regular letters from D -i- E -t- E -r inside BERN="capital" of Switzerland
Possible reason for booking manual worker before party (8)
I never did insist on emerald rings (5,2)
Fancy a round, stopping out (6)
I haven't cracked this one yet — but Fifteensquared have:
definition: "Fancy" as a noun for a thought or idea O="round" letter; inside/"stopping" NOT IN="out"
Threatening words worried lessee? There's nothing odd in that (2,4)
I haven't cracked this one yet — but Fifteensquared have:
w- O -r- R -i- E -d L -e- S -s- E -e, without any of the "odd" letters
Bit of a shower head in receptacle in a rubbish dump (8)
Type letters or click words in the clue