I found this very easy indeed at first with all but 3 answers written in after only 9 mins. A little slower getting those last 3.
Solving time: 14 mins
Notes on some clues below: happy to explain others if asked.
* = anagram
ACROSS
8 SOLE One of the sea areas used in the Shipping Forecast
9 MOUSSE How a Scot might pronounce ‘mouse’, I think
18 DI’S T (R) AUGHT R being one of the three Rs
22 LAV (END) ER
DOWN
1 I’M POSING
11 ERATOSTHENES (So earnest the)* Greek mathematician of old.
It’s certainly how Lord Rockingham’s XI pronounced mouse. “Hoots mon! There’s a moose loose aboot this hoose!”