Grand British housing wrecked sower's theories (9)
I believe the answer is:
guesswork
'grand british housing wrecked sower's theories' is the definition.
I can't judge whether this definition defines the answer.
'grand british housing wrecked sower's' is the wordplay.
'grand' becomes 'g' (G is short for grand as in a thousand).
'british' becomes 'uk' (Great Britain).
'housing' indicates putting letters inside.
'wrecked' indicates an anagram.
'sowers' with letters rearranged gives 'esswor'.
'uk' enclosing 'esswor' is 'uesswork'.
'g'+'uesswork'='GUESSWORK'
Can you help me to learn more?
(Other definitions for guesswork that I've seen before include "Speculation" , "Conjecture" , "Formation of opinion without definite knowledge" , "Supposition" .)