Simple - Do not use the old BT Yahoo sign in for your access to your user.name @btinternet.com address on the IPAD.
Although (at this date) the old BT Yahoo sign on can be used on your pc (laptop or desktop) it cannot be used on your IPAD - you end up with a blank screen with no explanation.
Use the http://home.bt.com/ (BT.COM) home page - click email (right hand side) and you will get a new sign on page.
Its looks like it has all to do with the BT migration of its BT Yahoo email to BT.com email and there has been no consideration for IPAD users.
Hope this helps. I am not generally a forum user however after 2 days waste on finding a solution on the IPAD it then took me ages on a BT Online Chat facility to come up with an answer and I would not wish this on anyone.
Hope this helps
Thanks - I did wonder if that might be the case but it would have helped if BT had put this info on the on the BT.com.
I can't say I like the new home page page. Being able to select content was a great feature, hopefully BT will add this back soon.