judging from satellite pics there are two clear connections t1-t2, maybe not both for pax
from the lhr interactive map, i think you'd take that long walk to the t1 gates way out past the el al lounge, as it seems that t2b is built onto the tip of this furthest point of t1 and uses the same long walkway to connect it to t2a, with t2a a side turning off the walkway
that puts the t2b united lounge about as far as it could get from the lr gates in t1 domestic, maybe a 2.5km round trip? even if there's a more direct t2a-b route, it's still a long way
for lhr ch i'd walk that far, but not for united club!