You are welcome. I hope it gets fixed.
Good morning Eric,
Sorry for the delay in getting back - unfortunately I still have the problem but I have got round it by logging into my BT account daily and deleting all the emails that have already been downloaded to my 'Mail' application so that they can't be downloaded more than once, also changed the Mail preferences to 'Download Manually'.
It is an extra little teradiddle but it only takes a few moments and I can live with that - thanks again for your help, Eric.