It would appear that they've taken their system down for an upgrade for an entire business day. I tried doing a transfer at 0815 today and I've just called them to be told that they expect the system to be available after 5pm.
On top of that, a transfer scheduled for yesterday hasn't been processed so instead of hitting my current account tomorrow, it won't get there until Friday. I've told them I expect a CHAPS payment in my account tomorrow but I shan't hold my breath.