The advantage EI have, is they are already up and running. BA, I assume would need to find extra aircraft (over and above their existing ones on the routes) and crews to operate the additional services. Of course they could hire EI to do it for them
Fair point epsomdog, I didn't really explain my rationale too well. EI will have a few aircraft making their way back to the main fleet once Little Red ceases. Supposing there was an agreement that EI utilise some of said frames on DUB/LHR and all traffic routed on EI aircraft with shared costs between BA/EI. BA can then slightly increase capacity to match actual demad with their own aircraft on routes where they are firmly established which are being vacated by Little Red.