British weather being on the wet side prompts idea (10)
I believe the answer is:
brainstorm
'side prompts idea' is the definition.
'brainstorm' can be an answer for 'idea' (I have seen 'Bright idea' mean 'brainstorm' so perhaps 'idea' could also mean 'brainstorm'). I'm not sure about the 'side prompts' bit.
'british weather being on the wet' is the wordplay.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'weather' becomes 'storm' (I have seen 'Violent weather' mean 'storm' so perhaps 'weather' could also mean 'storm').
'being on' means one lot of letters go next to another.
'the wet' becomes 'rain' (the wet can mean wet weather).
'storm' after 'rain' is 'rainstorm'.
'b'+'rainstorm'='BRAINSTORM'
Can you help me to learn more?
(Other definitions for brainstorm that I've seen before include "Sudden clever idea" , "Be creative" , "in which one's unable to think clearly?" , "Generate ideas; mental disturbance" , "Seek collective inspiration" .)