Excellent support from Apple
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I hunted about on the net but got nowhere so I went to https://getsupport.apple.com, made the appropriate selections, filled in the form and they phoned me in about 4 minutes.
For the next couple of hours the patient, non-judgmental bloke at Apple took me through a host of possibilities [several took a while to sync as my internet link is not the fastest] and in the end he solved it.
Brilliant free service from Apple.