Farm vehicle seen in Chelsea, they say (7)
I believe the answer is:
tractor
This clue is a double definition.
'farm vehicle' is the first definition.
(I've seen this before)
'seen in chelsea they say' is the second definition.
(as in the phrase 'Chelsea tractor')
(Other definitions for tractor that I've seen before include "Farming vehicle" , "Agricultural machine" , "Powerful farm vehicle for heavy work" , "Vehicle used on farms" , "Vehicle for pulling others" .)