Hillingdon BC boundary
@ Surreyman et al.
You can find the present Hillingdon Council boundary either on the Hillingdon web-site or on the Ordinance Survey election maps web-site. I've looked myself and the present boundary between the Royal Borough of Windsor & Maidenhead (RBWM) in the area of M25/J14 is the central reservation of the M25.
In 2009 when Labour announced the go-ahead for R3, they proposed another tidying up of the Heathrow boundary - which is why the maps provided by FlyingEagle21 show a Hillingdon extension around M25/J14.
Interestingly at the public display for R3 at the Renaissance / Ramada Hotel another Heathrow extension was exhibited for the inclusion of the A4 Budget car depot to the East of 27R; when I asked why, I was told it was a security matter .
Later we were told that if BAA wished to extend Heathrow over the Budget car depot, then they should purchase it in the open market and not under the excuse of a R3.