Just read the full thread and the requirement is for 2 x 30 kw boilers, so to be on the safe side assume boiler efficiencies of 85% the requirement is 60/0.9 or 67 kw net, assuming "wet gas" loss of 10% then requirement is for 67/0.9 or 75 kw gross. Don't know what the average gross CV of UK gas is but (I don't have gas) the last bill I saw (here) showed 11 kwh/M3 so meter requirement is, 75/11 or 6.8M3.
There is probably a published regional gas gross CV for the UK?.
There is probably a published regional gas gross CV for the UK?.