Originally Posted by BrianDromey

While that is usually the case, wont starting in the UK make the OP eligible for the APD? I suspect what has happened here is that the cancellation bots have been deployed, but the rebooking sweep has not occurred yet. OP - give the system 24 hours or so and you will probably find that your DUB-LHR leg has been reinstated. I've had similar happen to me with connections LBA-LHR and MAN-LHR, if the automatically rebooked segments are not convenient then call BA to ask for your options.