ACROSS
8 - Hat worn by ambassador – old and tawdry (6) - CHEAPO {C{HE}AP}{O}
10 - Topper is serious about gold (8) - SOMBRERO {SOMBRE}{RO<- br="br">->
11 - Quiet function held inside the Louvre perhaps (6) - MUSEUM {M{USE}UM}
12 - Behemoth falters badly making a bloomer (4-2-9) - STAR-OF-BETHLEHEM*
14 - Common rank in the military (7) - GENERAL [DD]
16 - Appeal of fairy tales (7) - IMPLORE {IMP}{LORE}
19 - Monarch say facing trouble reportedly, it could lead to chaos
(9,6) - BUTTERFLY EFFECT {BUTTERFLY} {EFFECT}(~affect)
22 - Dab of publicity (6) - SPLASH [DD]
24 - Total grind according to Spooner produced a pile of earth
(8) - MOLEHILL (~whole mill)
26 - Letters from oracle, verbose and witty (6) - CLEVER [T]
DOWN
1 - Choke and accelerator (8) - THROTTLE [DD]
2 - Professional whose job might be distressing? (6) - BARBER [CD]
3 - See flick, fave light romance (4,6) - LOVE AFFAIR {LO}{VE AF*}{FAIR}
4 - Agitated leopard is set free (7) - PAROLED*
5 - Take tips from Star Trek: Enterprise makers for a shoot (4) - STEM {S}{T}{E}{M}
6 - Hard covering an inferno after blow up (8) - NUTSHELL {->NUTS}{HELL} Reversal indicator not being accepted by Blogger, that's why it is in front of STUN!
7 - Don to take on responsibilities (6) - ASSUME [DD]
15 - Drill sergeant to arouse hostility (8) - ESTRANGE*
17 - Two PC makers upset being ordered to return (8) - RECALLED {->ACER}{->DELL} My COD
18 - Part of the problem is how to spot (7) - BLEMISH [T]
20 - Official from United Kingdom needs no introduction (6) - UMPIRE {U}{eMPIRE}
21 - German despot battered Herr and Frau heartlessly (6) - FUHRER {HERR+FraU}*