The proposal, as I remember it, was a third short runway to the NNW of Heathrow on the open land to the West of the Trust House Hotel. However, this was postulated in a Government report dated 1989 so I'm not sure whether this is still a viable option.
Regarding Northolt's continued operation, I played around with my radar picture today and, assuming a third parallel runway would be displaced by 1.5km, operations at Northolt would be untenable bearing in mind that the airfield is only 4.7km from 27R/09L.
Now the suggestion of just using Northolt as the third runway is not too bizzare. It's 5500' long and easily handles 737/757 type aircraft although range/payload may be somewhat limited.
I will dig out the old (public) report tomorrow and see if I can shed any light on the discussion.
Fly Safely..........
[This message has been edited by Whipping Boy's SATCO (edited 25 June 2001).]