This morning, in exasperation, I dangerously opted to press 9, the option to opt-out.
The computer immediately dropped the line.
[Update: this doesn't work, by the way. I was called again while writing this.]
I had thought that BT's free service, BT Call Protect, might be the answer. It does seem to have seen off some nuisance calls but you need to load it with the miscreant's phone number. The My BT app is so badly designed that this takes around five minutes.
"Hello this is an urgent announcement ..." are in any event more cunning. They change the number every time - in fact the apparent caller-ID isn't even well-formed, they're spoofing it.
In theory the telco the spammers connect to could police that. But there's a misalignment of incentives. It's more profitable to take the spammers' money as the telco doesn't directly suffer any financial consequences on account of the pain of the victims. Indeed, BT makes even more money by selling anti-nuisance-call products and services to its customers.
In this kind of market failure, only regulation works. Don't hold your breath.
There is a technical solution in the form of a sophisticated call blocker.
You set up the white list of numbers allowed through, and put hurdles (voice authentication, for example) in the way of everything else. A good device is not cheap.
Still, insensate fury carries you a long way. I put the order in this morning:
I know that configuration will be a pain. I know the excuse, 'this costs no more than a big shop at Waitrose', isn't completely compelling.
But short of taking the boys round, what can you do?
Update (Friday 3rd February 2017):
The trueCall device arrived lunchtime today. Setting it up proved pretty easy. Just a matter of reading the enclosed instructions carefully and plugging it all in. The lengthy part was uploading the 'star' list of numbers to be allowed through to the trueCall website. The format they want is CSV: phone number comma name, one entry per line.
It turned out that I had 37 phone numbers I wanted to allow through. Extracting them from Google Contacts and reformatting took a while (no embedded spaces in the phone numbers).
Still, done now and the device is synchronised to the website.
Now to enjoy unaccustomed quiet.
(I was going to write a piece on option-pricing and Black-Scholes this afternoon, but that will now be deferred to tomorrow, I guess).