I got sent this question last night:
"Anyone know why an ISP would say broadband issues are our wiring if the VDSL is rock solid and we only have PPP/IP connection drops, basically VDSL and phone are perfect and Internet drops connection with no errors counted. I can't see it being anything but router hosed. Wiring implies VDSL dropping too."
ISP is talktalk, using their 2 year old supplied router. Apparently the sync remains on the line remains constant, but the connection is dropped.
"It's [censored] the logs don't tell much apart from error counts (zero).
It drops in batches and then stays stable for ages, it last dropped at 7am yesterday it dropped 4 times in an afternoon"
Sadly no spare router to test with. I'm going to assume this issue has only started recently, although I can't confirm that. I've suggested PSU issues and using the Test socket, but have no first hand experience of TalkTalk's routers (not even sure what they supply).