Thanks for all of the interest in my original post.
I've done a bit more digging around the question of old LHR runways and found a 1956 Ordnance Survey map that clearly shows 3 parallel runways on the 15/33 axis. They are placed as follows:-
33R/15L runs from threshold of current 27L north-west to stop just short of the 09L/27R runway.
33C/15C runs from junction of current 23/05 runway with 27L/09R, north-west to a taxiway NORTH of 27R/09L.
33L/15R runs from just SOUTH of current 27L/09R runway (approx cargo area) north-west to just short of 09L threshold area.
If anyone wants a photocopy of LHR on this map send a PM with address or fax number. (I haven't got a scanner unfortunately).
HEATHROW DIRECTOR, there's only one reference to a 23/05 runway and thats the current one. However, there is the outline of what could be a 23R/05L runway (due to its width) but it's very short. This runs North-East from a point just north of the Perry Oaks sewage/water works.
Interestingly, having looked at the taxiway north of the current 27R/09L runway again on the map I see that there appears to be a large apron at the eastern end of it. I guess this would be roughly where the Heathrow Visitor Centre now stands. I have a recollection of a Pan Am B707 parked NORTH of the then 28R/10L in the early to mid 70's, but I've never managed to verify it. May be it was parked on this apron for some reason.
Does anyone have any recollection or documentation to explain this apron or the parked Pan Am B707 ?
airsmiles