A second ambassadorial greeting, flyingjonny, but it must have been a really bad flight for you. Two points from me:

There is something called "chef's chat", an A3 piece of paper loaded in the aircraft and that clearly indicates nut allergy items. So - without needing to go into the blame game - it was 100% avoidable. You can ask to see this, and indeed normally if the CSM was aware s/he would often bring it out to you so you could both work out a food programme that works for you.

Also, though I'm not a medic (there is one upthread!), I would reiterate the advice to - if necessary - call 999 even from airside to get an ambulance, though it does cause enormous difficulties for the airport management. For some reason BA staff in T5 are often oblivious to the fact that HAL pay for a unique branch of the NHS to work in Heathrow: they are absolutely there for you, you pay your taxes and PSC for this service. You will often see the paramedic branch of this service cycling around LHR, but somehow many gate agents haven't twigged why they are there. So you ask BA staff for help and they are stumped. If you approached a HAL member of staff (security or in a purple suit/dress) I'm fairly sure they would have got the paramedic off to you. This team isn't overworked, given my discussions with one of the members [and you should see what they think about BA staff!]

Though it shouldn't need this, I think self catering is probably the way forward, particularly for breakfast, the options are so restricted there except on the very long flights back to the UK.

Hope you made a full and happy recovery.