Thanks BOAC. That thread was more connected to a email password issue/scam I think, rather than to specific changes to BT Yahoo mail.
However, within that thread was a link to a posting by Milo in June
BT dumps Yahoo. This is what I recall and had me concerned at the time.
I'm assuming that as I use my accounts pretty well daily, I'm in no danger of losing my stuff. I've certainly had no issues and all is running smoothly but concerned about this latest 'ad' which does look real. I haven't responded to it.
I'm just unsure what to do or indeed if I need to do anything. Thanks again.