as its a 2005, jtdm, and it has only cost £155, i would assume it is therefore the earlier 140bhp JTDm, your local Alfa spares dept will clarify it for you if you giver them the numbers to run.
that would figure, as the later M-jet with the uprated injectors, and suited mapping, kicks out 150bhp, which has to kick more Co2, too, yep?
but don't worry or feel in any way inferior, its only at the outright peak i gather, the torque is nigh on identical at there respective peaks, and a decent remap will have you whistling up to 175bhp'ish from the 140bhp lump anyway.
enjoy it, it will be fab i'm sure
welcome to the converted, i hope you'll feel at home soon!