The radiators and hot water tank will be salvaged, but apart from that the whole central heating system will be torn out and replaced on the 22nd of next month. I'm seven grand lighter of pocket and will be living without a ceiling for another month. I do get two years complementary Homecare with it so I suppose that is equivalent to a 20% discount from one point of view.
Also, now I have had time to reflect, it would have been easy for Mick to ignore the damp cladding on the vent pipe, put up the ceiling, and trouser the fee, leaving me with a ceiling that would collapse with damp again in a few years, so props to him. He's cost himself money and inconvenience for my benefit.