They also tried to run an operation over the weekend but had to canx flights because of crew going sick for different reasons.
Take your pick of reasons as apparently this happens every year on the first weekend of July,
London Pride
Lions test
Wimbledon final
Henley Regatta
Madonna concert
Take That concert
Sunshine Sickness!
From CC News, last year that BA plan on approx 550 absentees on a normal day (no shows, sick, maternity etc). Over peak times such as this, they see in excess of 850