Solution to 7D has been deliberately left unsolved and is to be answered only by a non-regular / novice commenter, with proper annotation. Those who have answered earlier in the week, please give others a chance.
Open for anyone to answer, if not solved by 1 PM.
ACROSS
1 Primarily sexy mate turned on bar girl immediately (4-4) SLAP-BANG {Sexy}{PAL<=}{BAN}{G}
5 Smuggles exotic snakes (6) SNEAKS*
10 & 6 What diligent geologists will do to make every possible effort (5,2,5,8) LEAVE NO STONE UNTURNED [C&DD]
11 Extorts a definite promise from foolish son-in-law stifling daughter (5,4) NAILS DOWN {SON IN LAW}* over {D}
12 Impression made by English nationalist ranting about Government (9) ENGRAVING {E}{N}{RAVING} over {G}
13 Young bird of duck, beginning to leap into water (5) OWLET {0}{W{Leap}ET}
14 Whispers of women going astray, enthralled by dope (6) ASIDES {AS{wIDE}S}
15 Rat is over top of rusted grille (7) TRELLIS {T{Ru...d}ELL}{IS}
18 Hamper in cabin, extremely large (7) SHACKLE {SHACK}{LargE}
20 Dog at home stops crook (6) CANINE {CAN{IN}E}
24 Drug that arouses remarkable lust, mating endlessly (9) STIMULANT {LUST+MATINg}*
25 What may cause quivering lips to meet, expressing first sign of passion? (9) MISTLETOE {LIpS+TO+MEET}* Semi&lit
26 Overwhelmed by tackling a nasty parasitic disease of livestock (5) NGANA [T]
27 Director went up after drinking whiskey to sleep (6) DROWSE {D}{RO{W}SE}
28 Be able to lazily captivate date in a forthright manner (8) CANDIDLY {CAN}{IDLY} over {D}
DOWN
1 Collect rupees over large tray (6) SALVER {SA{L}VER}
2 Swilling ales again for relief of pain (9) ANALGESIA*
3 American in wild bender lets loose after take-off for fun (4,3,8) BEER AND SKITTLES {A} in {BENDER} with {LETS}*<=>{SKIT}
4 Sister thus returned to welcome hundred and one papal ambassadors (7) NUNCIOS {NUN}{SO<=} over {CI}
6 See 10 Across
7 Key left behind a parcel in retreat (5) A?O?L ()
8 Clean seats in compound outside institute (8) SANITISE {SEATS+IN}* over {I}
9 Gifted extraordinary toy (6) FIDGET*
16 Help design a hotel in property (4,1,4) LEND A HAND {END}{A}{H} in {LAND}
17 Admirable seed easily wins match, making a comeback (8) ESTEEMED {SEED}* over {MEET<=}
19 Phoney arrested by officers at Zurich (6) ERSATZ [T]
21 Regular boyfriend in filthy place, cuddling topless escort (6) STEADY {ST{lEAD}Y}
23 Relish breeze on top of observatory (5) GUSTO {GUST}{Ob...y}
Reference List
Girl = G, Daughter = D, English = E, Nationalist, Government = G, Women = W, Director = D, Whiskey = W, Date = D, Large = L, Hundrea and one = CI, Institute = I, Hotel = H, Million = M