Safari: lock 'Hide Reader'?

On my Mac (Mojave), if I go to BT.com and then sign in to my emails, 'Show Reader' is on by default, which is infuriating, because when I click on an email, it opens but almost instantaneously is overlaid by its text in a large font and any attachments are hidden. I then have to go to the View menu and select 'Hide Reader'. Is there any way that I can set 'Hide Reader' as the default setting? Any help much appreciated.