My post from the 28th highlighted my problem with the login to the talktalk.co.uk account page. That day I submitted an online help request via the site.
Today, 6 days later, I get an automated response saying they will respond in the next "5 working days". I'm not allowed to reply to this e-mail to tell them not to bother since the problem solved itself a few days later (as I'd predicted).
update: 17 July - still no response. HA HA