Go off at a tangent regarding son in lodgings (7)
I believe the answer is:
digress
'go off at a tangent' is the definition.
(I've seen this before)
'regarding son in lodgings' is the wordplay.
'regarding' becomes 're'.
'son' becomes 's'.
'in' is an insertion indicator.
'lodgings' becomes 'digs' ('digs' can be a synonym of 'lodgings').
're'+'s'='res'
'res' put inside 'digs' is 'DIGRESS'.
(Other definitions for digress that I've seen before include "Wander from subject" , "Go off the main subject" , "Leave the point" , "Wander from the point" , "Go off at a tangent" .)