It was a 6-pointed star arrangement and visible in these various places:
Cassini Maps - Online Historical Map Shop - High Quality Old Maps
The caption on this ismage is:
The pattern was used so two runways would always be within 30 [degrees] of the wind direction. Source: Heathrow Airport in 1955
Heathrow Airport History
If the airport had been allowed to expand naturally, we might still have two sets of parrallels! This aerial shows the pattern is still visible, although they are now (mostly) taxiways.
London Heathrow Airport (LHR) - Review - A lot of history