Times 26,270

Continuing a run of mostly very straightforward puzzles, clock stopped today at 7:25, helped by all the required general knowledge / vocabulary falling within my comfort zone, and much of it quite possibly learned from previous crosswords. A notable bias towards science rather than the arts today, which will please those solvers who claim (with some justification, I think) that it's almost always the other way round - no reason why classicists like myself should always be given a headstart. All in all, a very pleasant solve.

Across
1	SPEECHLESS - SPEECH(=elocution), LESSON minus ON.
6	IRIS - IRISH minus H{ospital}. Do these puzzles long enough and this is one of those definitions which are baffling first time round, and (you hope) always remembered thereafter as they crop up again on a regular basis. Well down the list of definitions of "flag" in the dictionary: a plant of the iris family with sword-shaped leaves.
10	SUCCUBI - U(=posh, from the Nancy Mitford lexicon) C.C.(cricket club) in [SUB (edit articles), 1].
11	PUBLISH - PUB, L{andlord}, IS H{ard}.
12	IMPOTENCE - I(current in scientific notation) M.P., [TE in ONCE].
13	GLOOM - G{ir}L, (MOO)rev.
14	RADAR - RADA (Royal Academy of Doing Acting Dramatic Arts) + R{uns}.
15	ZOOLOGIST - Z(today's unknown) + OOLOGIST(posh word for an egg expert).
17	EASTER EGG - E{nglish}, ASTER, E.G. G{arden}.
20	RELIC - ELI(the Biblical High Priest) in R.C.
21	TRUSS - TRUSTS minus {transpor}T.
23	PILLAR BOX - ILL AR{a}B in POX. A distinctive bright red, of course, though when Trollope (yes, that Trollope) introduced them to Britain, they were actually green.
25	EMPEROR - EM(a typesetters' space, twice the width of an en) PER(=for each) OR(=gold).
26	ANDORRA - AND O.R., R.A. Two perennial abbreviated soldiers, Other Ranks and the Royal Artillery.
27	SERF - reverse hidden in reFREShed.
28	MANHANDLES - N{ew} HAND(=worker) in MALES.
Down
1	SUSHI - (SHIATSU)* anagrammised without the AT. I suppose "local" course in that it's particularly tied in origin to a specific part of the world, despite the fact that nowadays you can have it for lunch in most UK city high streets.
2	ESCAPADES - E{astern}, ChAp in SPADES.
3	COUNTERMEASURE - double def., one of them a playful one based on the haberdashery counter (the sort with many little drawers underneath, reflecting presumably the need to keep your buttons and ribbons and things separate). edited to expand: as Derek and others discuss below, the specific reason for using this example is because there is a rule built into the top of the desk to allow the vendor to easily measure items which are sold by the yard (other units are available); is this actually a drapers' counter rather than a haberdashery? I am not expert enough to say, but I can certainly find this item, which illustrates the idea, and is definitely described as the latter.
4	LEIBNIZ - N{ot} in LEI(=currency of Romania), BIZ. His name came up on TV recently (I suspect an episode of Q.I.) as a candidate for being "the last man who knew everything" i.e. a gifted polymath at a period in human thought when we hadn't yet learned enough about the universe to make that impossible.
5	SUPREMO - SUP (MORE)*.
7	RHINO - double def., another one acquired from crosswords, I think, as it's a slightly archaic word (by which I mean nobody in my circle goes looking in their wallet for "rhino").
8	SCHEMATIC - (MATCHES)*, I{mpress} C{rowd}.
9	I BEG YOUR PARDON - (REGROUPINABODY)*.
14	ROENTGENS - O{ld} in RENT GEN, S{ociety}. The unit, unsurprisingly, named after the man credited with the discovery of 24 down.
16	ILLIBERAL - lots of numbers, and some Soviet history: 1, followed by several Roman fifties, LLL; and the NKVD (a forerunner of the KGB) was headed by BERIA, who is inserted with the 1 moved upwards.
18	EMPORIA - P{iano} in {M}EMORIA{L}.
19	GOLIATH - (TAIL in HOG)all rev.
22	UPPER - double def., one from the shoemaker, one from the pharmaceutical vernacular.
24	X-RAYS - X(=cross), "RAISE".