You are being totally ripped off. I'm not taking glee in saying this but they are running rings round you.That is what i think it may come to. Apart from the 550 for incidentals, they also want to charge me 1k extra for a few additional sockets and light fittings - i have to supply lights, switches etc. myself anyway. All i'm asking them for is neutral at switch and 45mm back boxes.
I'm really starting to regret paying on demand. I've already transferred over half the total contract price and they haven't even finished the loft yet.