Thanks izalco - you were spot-on.

Just spoken to BA. I was initally told that the return legs had been cancelled because the minimum connection time in London had been breached due to a schedule change. When I asked to be rebooked later or following day, the excuse was then that BA are no longer flying LGW-DUB, so I'd have to fly from LHR.

Thankfully got re-booked with an overnight in London, managing to keep the same flight in from LAX, and finding the no-one had yet grabbed my previously chosen UD seats.

So, apart from me sending a very snippy email to BA to complain about a total lack of communication over them cancelling half my trip, all's well that ends well.

Moral of this tale though is CHECK YOUR BOOKINGS, and regularly!