So...
...a little while after they moved to Google Mail it became a complete pig to use my Virgin account for anything Google related - namely my YouTube login for subscriptions and whatnot. Logging into YouTube or anything else Google related using my Virgin email address resulted in a highly convoluted - and broken as far as I could tell - process to somehow link the two. Without doing that it effectively stopped you logging in to any Google service with an existing Google account based on a Virgin email address.
End result was giving up and migrating all my subscriptions, settings etc from my Google account registered to my Virgin email, to my actual Google Mail account. Not the end of the world but a ballache.
Thanks Virgin/Google. There's nothing better than when giant companies make U-turns that waste my time. Much love.