This is just to raise awareness (if not solved by the morning) that the BT.com template header and menu bar formatting has gone wrong from around 00:14ish on 16/01/14. It may be a that a script or html style sheet have been altered slightly.
On looking at the debug console it looks like the server which contains the header.css stylesheet is not responding (error code 404 [not found]). The header html style sheet address is https://img01.bt.co.uk/s/assets/271113/css/header.css
Hopefully it just someone doing some site maintenance or updates.
not had any problems today - currently using chrome