Welcome Aboard....
Ashford is in Surrey, since 1965.... When they pulled the boundary across the Thames.
Middlesex has not existed since then....
Only the Post office used the term "Middlesex" after 1965 as an indicator to avoid confusion between Ashford Surrey... (Formerly Ashford Middlesex)... and Ashford Kent........
Until a year ago, then the Post office stopped using it. Tho it has the Postal district of Twickenham which is in Greater London.... Not used by anyone any-more except as an historical reference....
Glad you cleared that one up Rat-man.