Join Date: Aug 2011
Location: Barcelona, London, on a plane
Programs: IB+ Gold, TK E+, Hyatt Globalist, Marriott LTP, IHG Diamond
Posts: 14,182
Even though this isn't exactly what you asked...
I understand that EC261 no longer covers you when you are travelling on an EU airline but your itinerary departs from a non-EU country and arrives to a different non-EU country, with only the connecting point being in the EU.
You would only be covered under UK261 if you flew on a UK airline. Since BA handled the last two flights, you might get lucky claiming in MCOL against them. (even though realistically the delay is IB's fault)
Yet another Brexit own goal...