Back in 2011, I had VDSL installed in my flat. As part of the installation, the BT engineer replaced the faceplate on my master phone socket and also supplied me with a new modem:
Earlier this year, the modem developed a fault and I couldn’t get online. Annoyingly, this happened on a Friday evening, so A&A’s tech support had closed for the weekend. I got in touch with them on Monday morning, then BT sent someone out on Tuesday morning and I was back online by 09:30. So, I didn’t have internet access for 3½ days, but if the same problem happened midweek then presumably it would be resolved more quickly.