After an hour there was no sign of the power coming back, so I decided to phone up and find what was happening. However, who should I call? I get my gas and electricity from British Gas, but I switched over to e-billing a while back so I couldn't get the phone numbers from my bills without power for the computer to check my email. I dug out the Yellow Pages and found their number in there. Their listing included the National Gas Emergency Service (0800 111 999), but that was irrelevant because I didn't smell gas. Of course, due to my anosmia I'd never smell it, but I'd been able to light a couple of candles without the air catching fire. They also had a freephone number for people wanting to switch to them, so I tried that. As I'd hoped, this got me into their menu system ("Press 2 for any other service"), but then it just said that their office was closed. The message provided the number for gas leaks, and then said: "For power cuts, phone your electricity distributor. Their number should be in the phone book." Great, thanks.
The problem here is that I don't keep track of all the subcontracting arrangements between different suppliers: I know who I pay my bill to, but I don't know or care who they get electricity from. However, without knowing that company's name, I suspected that it would be difficult to look up their number. Fortunately, I was able to find an old paper bill from 2009 (yay for clutter!) which said that I was with EDF; that bill also gave a freephone number to report power cuts (0800 783 8866). When I phoned up, the person who answered the phone gave their company name as "UK Power Networks". Now that power's back, I've looked through the pdf files for newer bills; it turns out that my supplier switched from EDF to Seeboard in 2009, then switched again to UK Power Networks in 2011. However, they've kept the same number all the time, and UK Power Networks has a big advert in the Yellow Pages under "Electricity Suppliers". The advert also says: "Alternatively text 'Power' then your postcode to 80876 (e.g. Power SW11 1UW)". I haven't tried that, but it implies that they act as a central point of contact for all the power companies in the UK, which is sensible. So, phone books aren't quite obsolete yet (despite what Dork Tower says), and British Gas are providing a rather poor service by not giving out that phone number themselves.
The person on the phone said that there had been a problem earlier, but the engineers had reported it fixed at 16:30. My power went out at 17:00, so I think that was unrelated. She then found a report from someone in the road behind me which seemed more relevant. They'd sent people out to the relevant substation, and they estimated that power would come back at 20:30. (This phone call took place at about 18:00.) She took my mobile number and said that I'd get automatic updates on progress as they went along, which is quite a clever idea. If the problem wasn't fixed by 21:00 (and I hadn't received any relevant updates) then I should call again.
By 19:00 I hadn't had any messages so I went out to the local chip shop. (I couldn't cook at home without electricity.) I got back at 19:20 and heard my burglar alarm going off, which meant that power was back; I don't know how long it had been ringing for, but hopefully not too long. I turned it off when I got inside, and then started resetting all my clocks (like I do in the GMT/BST changeover). Just as I moved onto the second clock, the power went off again and my alarm started blaring again. The power came back on about a minute later, so I turned off the alarm again. I was a bit concerned that it wouldn't do my computers any good to keep getting shut down abruptly, so I really do need to replace my UPS batteries. Still, they seem ok for now.
At 19:32 I received my first text message: "Engineers have arrived on site to carry out initial investigations; the reason your power is off is a blown fuse at your local substation. Work will continue as quickly as possible to get power back on." Better late than never, I suppose. I then got a follow-up text at 19:48: "We're very sorry for the loss of your electricity today; all power should now have been restored. If you are still experiencing problems with your power please call us on 08007838866." I've also received an incomplete "Welcome" message: it was timestamped at 18:20, but I didn't receive it until 21:50. I think that's partly because my reception is a bit iffy at home, but it's odd that the later messages arrived sooner. I think the principle is good, but the implementation isn't as robust as it could be.
Anyway, the moral of this story is that I need to make a list of emergency contact phone numbers and keep a hard copy that I can refer to during a power failure. I advise other people to do the same, and I'd welcome any suggestions of other useful numbers to include in the list.
Edit: The power went off again at 23:40. I phoned UK Power to report this, and they said that the earlier fuse replacement hadn't worked so the engineers needed to shut it down for emergency repair. I mentioned that I hadn't received any updates after the last "Everything is sorted out" text message, and the person on the phone said that they don't send text messages out after 22:00. I assume that's because they don't want to wake people up, but maybe an email distribution list would be a better option. If I get some kind of advance warning that the power's going off then I can plan around it. I asked how long it would be off for, and she said that it would be a 4 hour window, i.e. they could guarantee that it would be back by 03:30 but anything else was guesswork. Fortunately the power came back on again about 10 minutes later, so I didn't have to get up in the middle of the night to turn off my burglar alarm etc.