I fly LHR/BFS regularly and can't remember when I last had any significant delay.
Pretty ridiculous to say that you haven't had any significant delay when Aer Lingus pulled out from this route last October.
That rather depends on whether the OP was using
BFS (IATA airport code) = Belfast (Aldergrove/International)
or
BFS (IATA metropolitan code) = Belfast (all airports)
Given that the context was his flying
regularly to Belfast, it's not hard to work out which he must have meant.
Looking at the stats for the last couple of months, they are pretty grim though - fewer than two-thirds of BA's Heathrow-Belfast flights were airborne within half-an-hour of the STD.