Is able to include England's capital, as a city (4)
I believe the answer is:
caen
'a city' is the definition.
(I have seen 'French city' mean 'caen' so perhaps 'city' could also mean 'caen')
'is able to include england's capital' is the wordplay.
'is able to' becomes 'can' (if you can do something you are able to do it).
'include' indicates putting letters inside.
'capital' suggests taking the first letters.
The first letter of 'englands' is 'e'.
'can' enclosing 'e' is 'CAEN'.
'as' is the link.
(Other definitions for caen that I've seen before include "City in Normandy" , "French city" .)