B
Blackcatgas
I concur with q-plumb, its a bit late at night now to calculate it + Iam full of strong lager, either way, Halstead or worcester your going to need to uprate the gas pipe size, (cant this be run outside? etc) so you may aswell go for the worcester out of the 2 boilers.without even looking what the gas rate would need i would say at least part of that would have to be 22mm due to amount of bends and length especially with a gas oven and hob coming off it.
go for the worcestor....