I live right next to the FTTC cupboard in central London, and I, too, am plagued by sporadic outages. One night recently, I had 40 disconnections at 2am in the morning within the space of 20min.
My ISP (Uno) told me they can't do anything unless the line is "actually" down, which of course it wasn't when they checked it.
I'm lucky enough to have one of SamKnow's boxes, which actually records those outages into lovely graphs. Still, apparently the data SamKnows records is not suitable evidence to prompt an investigation - if I need a reliable line, I should get EFM I've been advised...