Thanks for all the replies to my original question. Some 3 weeks later the car is back from a good, if slow, mechanic.
3 valves were too tight and one too loose, timing too retarded and the noise remained. At this point suspected fan as valves sorted. He took it for a 'brisk' drive and on his return the noise had gone! I guess it was the tin around the fan, I will keep an eye on it.
38 degrees here, unusually warm, car running really well, so I guess I better go and enjoy it!
Tim
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