This is a reply from a friend who's father used to work for Fairey's at Hayes.
"My father, John Chinery, worked at Fairey (and Westland) from 1946 to closure of the latter, and ran the Fairey Retired Member's Group until his death in 2000. I actually live across the road from the Hayes site so can vouch for the latest situation. Mercedes have come and gone, as have Marks & Spencer and the occupant of the largest part of the site (now a trading estate) where the old canteen was, is Nippon Express air-freight company. At least 70% of the site is vacant, including the large warehouse that was Merc and Marks!
The final assembly of most Gannets was completed at Northolt, but at least a dozen of possibly the early aircraft were towed to Northolt from the factory by public road in the dead of night on their own wheels with wings folded. I remember seeing pics in the local newspaper at the time!"