I've been reading up on this and it appears that BT's server will only let you use the older version if it detects that your screen resolution can't handle the new one.
So the trick is to (temporarily) drop your screen resolution, go into your mail, accept the option to permanently use the old version (which puts a cookie onto your PC, so that BT's server will always supply that version in future) and then restore your screen resolution to its former setting.
Instructions are in this post from Ocean:
http://community.bt.c...ail/m-p/389901#M14320
Chris