Two points:
1)
BA shorthaul suffers disproportionate knockons from disruputions because the aircraft, tech crew and cabin crew are all rostered separately. Crew and aircraft seldom stay together for the next sector out of LHR . This is compounded by cabin crews minimum turnaround time agreements which illogically and expensively treat LHR differently from any other point on the network.
2) Never mind 3 runways, the published 1947/48 plans for LHR showed nine runways, six south of the A 4 and 3 in a triangle between the A 4 and where the M4 now is. 2 of the southerly 6 would probably have had to go to make way for the Central Terminal Area, but it was still a pretty impressive collection. Harmondsworth and Sipson were scheduled to disappear via compulsory purchase orders. All of this was scrapped around 1954 as the bureaucrats and politicians had by then decided that aviation needs would never grow that much and they would rather spend the money on the NHS. How times dont change.