Everything is fixed, I have a landline again!
To clarify for others, once I'd realised the landline wasn't working I checked all the cables were connected properly, I checked that the phone was fully charged and operating, I checked that there wasn't any obvious damage to cables leading to the wall-mounted socket, and I tried different handsets. Nothing gave me a dial tone. I could ring the number from my mobile and I would hear a ringing tone on the mobile, but nothing from the phone connected to the wall-socket. I checked service status in my area and there were no problems reported.
Having done all that, I requested an engineer appointment through the forum. @Akua_A was very helpful - they checked a few details with me, ran some checks from their end, and booked an appointment for me. My engineer, Stephen, turned up this morning, enabled the phone connection on the hub, and ran a few tests using my existing phone handset. Everything's hunky dory. The wall socket is a bit redundant now but who cares!
Tony