Not too difficult, I found, solving time 22 mins.
* = anagram < = reversed
ACROSS
1 OPUS hidden
4 Long John SILVER WAR E
10 LE AN-T O Collins confirms it can be a roof as well as a shed
11 BILL (Clinton) YO (as, in ‘Yo, Blair’ when Bush and he were in Russia, if I recall) Definition ‘very much’. Collins confirms it can be spelt without a hyphen
12 EDGEHILL (I held leg)* English Civil War
13 HOLY HEAD
15 (u)SURER
16 C(H) ART Spent too long thinking the vehicle must be ‘car’
17 BEST OWER Favourite clue, though a nit-picker might suggest it should be ‘worst ower’!
19 NOBLEMAN m in (Lebanon)*
20 B (E’ER)-UP Australian slang, new to me, that I worked out from the wordplay . ‘Rowdy’ suggested an anagram, though ‘pub’ is just reversed.
22 A GAR A GAR As an experienced solver got this straight away though I’ve never come across it or its wordplay components in ‘real life’
23 PEDESTRIAN Excellent double definition
24 TIER Robert “Tear”
DOWN
2 PROV (IS) O (st)
3 SHIRLEY MACLAINE (Archie – silly name)* Weak on films, but I’d heard of her.
4 SCH MO US usage
5 LAP HELD pal< Another name for a ‘laptop’ computer i.e. PC
6 EU LOG (r)ISES
7 WEATHER FORECAST (Two teachers fear)*
8 RATT(L)ER
14 ESTA (MINE) T(e)
16 C (HORAL) E
17 BEN (GAL) I (n)
18 EMU LATE ape (vb)
20 BRA (W)N w = with
22a Agar-agar – I believe used by vegetarians to make jellied desserts as, unlike the branded ones available in the supermarkets, it contains no animal product.
You missed out 9 across: polish up
Two things struck me about this: the totally brilliant 20dn, which left a slight doubt since I wasn’t sure that bran was cereal, but it is, so the clue is the best of the week in my opinion. And I wasn’t very happy with ‘unrestricted’ to mean ‘curtailed’ in 14dn.
I agree with Wil about ‘unrestricted’. I think it should indicate removal of first and last letters rather than mere curtailment.