Official information about posh dwelling-house (8)
I believe the answer is:
messuage
'official information' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'posh dwelling-house' is the wordplay.
I cannot really see how this works, but
'posh' could be 'u' (abbreviation for upper-class - opposite to non-u) and 'u' is found in the answer.
The remaining letters 'message' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'about' is the link.
Can you help me to learn more?
(Another definition for messuage that I've seen is " House with outbuildings and land (law)".)