LHR did have six runways -on basis one runway is a strip of concrete not recip directions on one strip
09/27s were there ( 10.28 in those days)
05/23 was there as 05R/23L (but seldom used today) had a parallel 05L/23R -I know that because it went right over my house sw of the field
There was another pair aligned NW -SE completing the famous Star of David pattern. I think the more westerly one of these vanished very early on and maybe was never finished but I remember as a child -I grew up immediately south of the airport-seeing landings on the more easterly one.
Te 05L/23R was clsoesd when terminal 3 was built in the late 1960s I think and the others are still there today so LHR did have at least 5 and for a short time 6
PB