Good news: as suggested by Anthony I emailed BT's chief executive, Ben Verwaayen, in an attempt to get my phone line installation sorted out some time before the next ice age. He responded within hours and put me in touch with a manager who arranged for an engineer to call the next day. The engineer -- in exchange for only two cups of tea -- very competently installed a new phone line. It'll still take bloody ages to get DSL installed, but whatever.... In any case, I'm impressed.
(I've had other -- much worse -- customer service experiences lately. I won't inflict them on you, but some advice: never, ever, ever buy anything from `Twenty-Four Seven Electrical'. They are incompetent lying scum and deserve... oh, I don't know, all sorts of unpleasant things. Also, if you have the misfortune to have bought something from Dabs Electronics lately, you'll have noticed that they don't have customer service phone numbers any more. However, there is still a phone number in the WHOIS record for their domain name, which puts you through to someone in their technical support department. In case they remove it, the number is +44 (0)1942 853488.)