I'm replying to my own question here because after a further half hour searching via the Site Map I found a back door way in to get at webmail.
Once I found a way to get to Email INBOX and logged in, I made a note of the URL that was required to access it. I found the following path:-
O2 Home; Services; Messaging; Email; O2Webmail; INBOX.
When I went back and tried to access it from that path going to O2 Home page I could find no SERVICES on the home page as a link at all. So I went back to the EMAIL login by the previous path and logged out, and then dragged the URL to my desktop so I can use that to access this hidden link.
www.o2.co.uk/myo2/emailI must apologise if anyone reading my post, thinks my query was a tad grumpy, but I hope you'll understand that it is still a stonking great waste of time trying to find the webmail login. There should be a link like they have on BT Yahoo, straight to it on the front page (in the banner at the top). I personally think this is a case of over streamlining of the o2 site. From my point of view having done 14 years of web browsing I think I can say with all honesty the O2 site still is far from right and not the least bit user friendly.