Del949, I am with you, I feel sure they use the smallest writing in the longest document to make you give up reading their t&c. I was on holiday resonantly and there was a solicitor with us and I asked him if he read the T&C before booking and he gave me an emphatic no. I always intend to but glaze over after a few paragraphs

It seems the easiest solution is for the OP to see if his Mum can change her date for hospital admission.
As its not until August the hospital will probably be able to give another date or even a cancellation.

I had to make a change to my hotel booking in Mexico last summer after BA dropped flights and changed days. I contacted bookings4u who told me they would have to cancel my booking and start again. How much extra did I have to pay? Nothing.
Whatever the ops terms and conditions say, it is a rip off. By all means you do need to pay to change flights etc but it doesn't cost £1300. Also remember some of the costs are are taxes which should be refunded IMO.
Explain to mum and ask if it's possible to get hospital to change dates, assuming of course that it is something can be delayed.
Good luck and keep us informed.
You can at least have the knowledge that you will have highlights to others the pitfalls to others and I for one will steer clear of TC and their not so flexible holidays

Fiona, there's often a big difference between whether and how changes to hotel bookings can be made in the event of the airline cancelling your flight compared to you needing to making changes to flights. How confident are you that if you had wanted to change the days of your flight that BA would have been as accommodating and by implication the agent, unless you had paid for a full fare, open ticket that allowed for such changes?

SM

I have alsi had to change at very short notice the cheapest economy long haul tickets wirh BA. Thw first time a couple of years it cost us £200; and that was done 24 hours before original departure.