House in Home Counties, north of motorway (4)
I believe the answer is:
semi
'house' is the definition.
(short for semi-detached)
'home counties north of motorway' is the wordplay.
'home counties' becomes 'SE' (Home Counties in the South East of England).
'north of' says to put letters next to each other (in a down clue, some letters go above others).
'motorway' becomes 'MI' (resembles M1, English motorway).
'se'+'mi'='SEMI'
'in' is the link.
(Other definitions for semi that I've seen before include "Prefix meaning half (4)" , "match, the last but one?" , "Not quite the biggest tie" , "Style of house" , "House; match" .)