OP
AP Electrical
With no easy way coming forward to isolate the problem, I took the simple route and rewired the 3 lights. Seems to have solved the problem and probably the safest option given the circumstances although I've now got a wall to patch up.
Thanks to those who tried to help.
Nice one iangorrie, now don't forget to inform LBC as kitchen is considered a special location and you've rewired a circuit.
AP