Thanks for everyones input on this. Admittedly I was wound up when I was posting. It turned into a travel nightmare so here is a quick update.

We were in CUN for approx 11:30 for our 13:59 departure. By the time we arrived at the airport it had been pushed back to 15:00. 12 further updates followed with constant pushbacks on the departure time. Eventually re-routed for DFW with an overnight stop. The airline didn't take responsibility for the hotel despite the agent confirming this would be arranged at DFW. They have offered vouchers for the various troubles (I had a list - genuinely the worst treatment I have ever experienced from an Airline and I have flown United, Easyjet and various Euro budget airlines) but are still refusing to accept responsibility for the accommodation. Waiting on a further reply.

One positive so far from this... I was credited with the tier points for the extra flight, which unexpectedly pushed me into BA silver/OW Sapphire