For a couple of days my super duper BT inifinity broadband had been acting up, and then it stopped working.  Last night I phoned the helpline number and, after the usual round of button pressing, spoke to someone who organised some checks on my line and confirmed there was a problem (well, I already knew that!).  She then arranged for someone to come today and sure enough, half an hour into the 5 hour period, the man arrived carrying a new openreach modem... 'that's what it'll be' he said, 'there were problems with the first batch and now they've overcome it.  I know it looks the same but it's not.' 

So he fitted the new modem - and attached it to the wall which he said the first guy ought to have done but didn't - and, lo, I have my super duper infinity broadband back again.

It's easy to find fault and to complain, but my problem was dealt with quickly and effectively, so I am happy to say 'well done BT.'