It's more often than not cheaper to connect via LHR & not just for shorthaul either.

I often compared EI’s premier fares to JFK, BOS, or ORD to an ex DUB/ORK fare with BA in CW. The difference can be quite large in BA’s favour & you get a lot more bang for your buck with CW than Premier.

It’s an awful pity that EI have never offered a discounted Premier fare like BA’s “I” class. Hence I’ve never yet flown Premier with EI across the pond, much & all as I’d like to try it out