More intelligent British having longer showers? (8)
I believe the answer is:
brainier
'more intelligent' is the definition.
('brainy' can be similar in meaning to 'intelligent')
'british having longer showers?' is the wordplay.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'having longer showers?' becomes 'rainier' (with more rain).
'b'+'rainier'='BRAINIER'
(Other definitions for brainier that I've seen before include "smarter" , "more clever!" , "More intelligent (colloq.)" , "With a higher IQ?" , "appearing brighter" .)