Across
Daily for example reversal of cost (6)
Hot air from gentleman accepting compliance with companies going back and forth (8)
I haven't cracked this one yet — but Fifteensquared have:
SIR (title for a gentleman) containing C (abbreviation for compliance, in physics), then CO (abbreviation for company) reversed and another CO forwards (companies going back and forth). A hot wind, typically one coming from North Africa into Europe.
Tell say when demonstrator loses his head (6)
I haven't cracked this one yet — but Fifteensquared have:
[m] ARCHER (one who goes on a protest march = demonstrator) without the first letter (head). For example William Tell, Swiss folk hero, pretty handy with a bow and arrows.
Baltic city into cooking pasta (8)
Boy reflected about hot Indian food (4)
I haven't cracked this one yet — but Fifteensquared have:
LAD (boy) reversed (reflected), around H (abreviation for hot). Indian word for lentils or a dish made from them. The spelling “dhal” is perhaps more common and works just as well with the wordplay, so we need a crossing letter to sort it out.
Gents maybe endlessly promiscuous (4)
Prominent scientist not a German mug (5)
I haven't cracked this one yet — but Fifteensquared have:
[ein] STEIN (scientist Albert Einstein) without EIN (a form of the indefinite article “a” in German). An earthenware beer mug.
Sweet treats served by London hide-outs (7)
Actor Paul who played a little role getting the red-eye (4)
I haven't cracked this one yet — but Fifteensquared have:
This looks like a double definition, though there may be more to it. There’s a US actor called Paul Rudd, who has appeared in a lot of films and TV shows, but I don’t think I’d recognise him from anything I’ve seen; and there’s a fish (genus Scardinius ) that can be called a rudd or red-eye. I don’t know what the words in the middle are intended to add, unless they’re pointing to a particular role that Rudd played? UPDATE: Matthew Newell (comment 3) points out that Paul Rudd played the “little” title character in the film Ant-Man . I thought it might be something like that.
Grocers intrinsically backing sustainability label (3)
Emperor overwhelmed by part of Soviets' army (4)
Prodigal son to hang former head of state (7)
Small lake surrounds university enclosure (5)
I haven't cracked this one yet — but Fifteensquared have:
POND (a small lake) around U (abbreviation for university). An enclosure for animals, especially for holding strays until their owners come to claim them.
Summit of Twitter these days following Apple regularly (4)
I haven't cracked this one yet — but Fifteensquared have:
X (the social media platform that hasn’t quite shaken off its former name Twitter, so “Twitter these days”), following alternate letters (regularly) from A [p] P [l] E .
Downfall of some nepotistic old world leaders (4)
Unwell in old island state (8)
Expedition from South Africa to remote India (6)
Woodman in favour of new trees (8)
Scoundrel ordered gallon after gallon (6)
Down
Caught dealer one who trades in wicked goods (8)
A school lecturer brewed strong drinks (8)
Dull elegist by the sounds of it (4)
Small boy in audition goes over lines randomly (12)
Shops aired dismally romantic pieces of music (10)
Old boxer's manager gained zero (6)
I haven't cracked this one yet — but Fifteensquared have:
COPER (one who copes or manages = manager) with an extra O (zero). Henry Cooper, British professional boxer in the mid 20th century.
Should a vegetable grower know his well? (6)
Pro establishment bringing jam round at (12)
I haven't cracked this one yet — but Fifteensquared have:
CONSERVE (jam = fruit preserve), around AT + IV (4 in Roman numerals). Conservative = inclined to keep things as they are = in favour of the establishment.
Insisted Democrat worked on Southern rebels (10)
I haven't cracked this one yet — but Fifteensquared have:
Anagram (worked) of INSISTED + D (abbreviation for Democrat), then S (abbreviation for Southern).
Troubled attendee unable to take a bite (8)
I haven't cracked this one yet — but Fifteensquared have:
Anagram (troubled) of ATTENDEE . Edentate = toothless.
Tanning ex-PM in government (8)
Dandy left inside joint (6)
I haven't cracked this one yet — but Fifteensquared have:
SPIFF (dandy, as an adjective = smart or dressed-up), with L (abbreviation for left) inside it. Joint = spliff = a cannabis cigarette.
Senior servant still essentially alert (6)
Lady singer out to lunch (4)
Type letters or click words in the clue