@sotonsam:
Now there's a sight I am all too familiar with! I am surprised that there are so many of these shells still existing (I guess that just demonstrates its build quality). It will be sad to see them go out of service when G.fast is rolled out.
An HG612 unlocked may be a good if you want to view and collect stats on your line's performance (once unlocked, which is a somewhat easy task with plenty of documentation). You can typically find them used on the bay for under £10 posted. I personally bought a version 1 Billion BiPac 8800NL to use as a modem with PPPoE bridging, and you can almost always pick up used for under £25 as an auction including delivery (sometimes under £20 if you're lucky). I just plug an Ethernet cable into one of the other ports of the router from another NIC on my PC to retrieve the stats from Web UI, Telnet and SSH.
Probably may be better and cheaper options to pick up a modem, but for me the v1 8800NL is stable and has a decent Broadcom chipset. And if my main router dies or has issues, I can use the routing and wireless capabilities on the 8800NL as a fallback.