mail forwarding not working

I routinely use my BT email address and have all mail forwarded to my iCloud email address. Within the last week I noticed that some expected emails were not arriving either in mac mail or on my iPad. I have contacted BT who say there is no problem at their end. If I set BT mail to forward only I don't receive the mail. If I set it to forward and store I receive two copies of the email - one direct to my BT email address and one forwarded to my iCloud address.

Can anyone help with this? I have not changed any email settings before experiencing these problems.

I don't want to store email in the BT webmail inbox, as deleting mail on my iPad would not also delete it in the webmail inbox.

I am using the latest version of Yosemite on a mac mini.

Thank you