I arrived in Heathrow yesterday 2.5 hours before my flight to a huge queue stretching outside the terminals into the parking lots. Mortifying to see. To my surprise I was past security in about an hour.
I was in that self same queue and also made it through surprisingly quick, only for my flight to Frankfurt being cancelled. Back at LHR now for round two.
Lucky you didn't go from Luton - there you'd have a bad airport time AND your flight cancelled (followed by more bad airport time).