There are very concise clues here, and lovely surfaces (I’ve commented appropriately below), and despite the interruptions, I thoroughly enjoyed this from Des.
Across
1 Fantastic sort of light: legendary (6)
FABLED – FAB (FABulous = fantastic) and LED (Light Emitting Diode – sort of light).
4 Important meeting with German on the whole (6)
SUMMIT – SUM (the whole) with MIT (German for with) ‘on it’.
8 Wildly boo a preacher, vicar initially blameless (5,8)
ABOVE REPROACH – Anagram (wildly) of [BOO A PREACHER] and V{icar} (initially). Just as our current Prime Minister described the Monarchy in last week’s election debate!
10 Prestige without end, so duke reflected (5)
KUDOS – Reverse (reflected) hidden, in SO DUK{e} (without end). Kudos comes from the Greek word for ‘glory’, and means credit, fame, renown or prestige.
11 Fail to broadcast (4,3)
GIVE OUT – Double definition.
12 Note girl, bourgeois (6,5)
MIDDLE CLASS – MIDDLE C (note) and LASS (girl). Perfectly concise clue!
16 Adult FM broadcast for land near estuary (7)
MUDFLAT – Anagram (broadcast) of [ADULT FM]. Nice surface!
17 Strikes on the wrists? (5)
CUFFS – Double definition.
18 Inadequately organised foreign articles, pruned in advance (13)
UNDERPREPARED – Slightly tricky parsing here. I read it as UN and DER (foreign articles, French and German respectively) and something pruned in advance might be PRE-PARED. The coincidence of pruned also being an anagram of the first 6 letters of the answer made me think for a moment or two.
19 Rather dull line in food (6)
DRYISH – RY (short for RailwaY) is the line, which appears in DISH (food).
20 Fashions in time followed by tears (6)
TRENDS – T{ime} followed by RENDS (tears – the verb to rend, rip or lacerate, rather than the noun referring to the products of weeping).
Down
1 Cuts of meat, tart, starters of kedgeree, salad (6)
FLANKS – FLAN (tart) and K{edgeree} and S{alad} (starters).
2 In the tolerant fashion of one planning Norfolk holiday? (5-8)
BROAD-MINDEDLY – The Norfolk Broads are a popular holiday destination in the East of England. If one were planning such a holiday, one might be described as being BROAD-MINDED.
3 Game of rugby to start late, as likely as not? (5)
EVENS – Seven-a-side rugby is a popular stripped down version of the more famous 15-man game. If the first letter is moved to the end (starts late), seven becomes EVENS. If a future event is as likely as not to occur, its odds of happening are said to be EVENS.
5 Solve value n, somehow about right (7)
UNRAVEL – Anagram (somehow) of [VALUE N] and R{ight}.
6 Warden Amos off touring plant (6,7)
MEADOW SAFFRON – Anagram (touring) of [WARDEN AMOS OFF]. If you are like me, your heart sinks when you see a clue defined as one of the millions of available plant species. In this case, though, the anagrist gives little alternative. MEADOW SAFFRON (also known as naked lady) refers to the autumn crocus.
7 Note about a popular song in S Pacific island (6)
TAHITI – The note is TI (from doh, ray, me, fa, so, la, TI, doh). This surrounds A HIT (popular song).
9 Eg, Great Britain consumer acquiring kitchen implement (3-6)
EGG-BEATER – EG (e.g.) and GB (Great Britain) followed by EATER (consumer).
13 Girl displaying knowledge in parties (7)
DOLORES – LORE (knowledge) inside DOS (parties). DOLORES is a delightfully old-fashioned girl’s given name that is hardly seen these days in my experience.
14 Inspired film about Edda appearing regularly (6)
IMBUED – Alternate letters (appearing regularly) in {f}I{l}M {a}B{o}U{t} E{d}D{a}. Lovely surface again.
15 Words from actors: like when Caesar about to die? (6)
ASIDES – AS (when) and IDES (when Caesar was about to die – the IDES of March).
17 Carbon copier for skip (5)
CAPER – C{arbon} and APER (copier). To CAPER is to leap or skip like a goat.
Biffed quite a few
Obscure parts – RY, FAB, LED, TI (not TE?)
GIVE OUT – is this a definition of fail?
Hate the plant ones – had to wait until all but 4 letters!
Nick