In any exceptional event in the UK which affects flow control, the knock on effect normally does take days to recover. When Heathrow loses both runways for 15 minutes and then is single runway for a further hour then the delays can be felt up to 3 days after. Exactly this occurred following the emergency return of the BA flight to Oslo after it lost the engine cowlings on departure. It wouldn't have made any difference if Heathrow had any more runways in operation at the time, purely due to SAFETY landings and departures were stopped. That is exactly what happened at Swanwick, measures were taken to provide ultimate safety, and then as the system recovered, the traffic was gradually increased again.
Who is at fault? Anyone who has an open mind will see exactly what the main UK ATC union has to say on the subject
here on the Prospect website