Thanks again all for the replies. Providing the IR is still good on the conductors I don't consider it to be 'unsafe' to install class 2 downlights. I have often replaced rusty old metal class 1 downlights in a bathroom that weren't suitable for the area, and where no cpc was present, with intergrated downlights suitable for a bathroom (not requiring a cpc), and I will continue to do this should the situation arise as I have clearly improved the safety of the installation, but it appears some sparks would refuse to do this which frankly surprises me.
I find it slightly bizarre that it's acceptable for a circuit to borrow a cpc from a completely seperate circuit.
As already mentioned, I shall offer the particular customer I referred to, the quinetic solution.