Originally Posted by corporate-wage-slave

The 5 hour rule is correct. But on the face of it you can claim EC261 delay compensation, assuming you are delayed more than 3 hours into LHR. This is because you appear to have asked to be transferred to an AA service, which had space, BA refused and thus "LE versus TAP" applies. Let's see how late you are into LHR however, and assuming LHR is your end point.