We have spent the better part of a decade going on about caller ID. Sending valid CLI, blocking the invalid stuff, dipping numbers to check they are real, alive, and able to take a return call. Most of that work is aimed at the obvious scrotes, the spoofers and the offshore dialler traffic no honest network should carry. But the longer you spend cleaning a thing, the more you notice the smudges nobody else is looking at. Here is one we cannot un-see.
Start with why a marketing operation has to show you a number at all. It is not decoration, it is accountability. The rules make a marketer present a contactable line so that you, the person on the receiving end of a call, can work out who rang and ring them back. Being reachable is the price of being allowed to call strangers.
Now watch it unravel, quietly and entirely within the law. You ring the number back, and because you have had quite enough of these calls, you withhold your own number. You are perfectly entitled to; that privacy choice is protected, and not only by PECR but within the CLI rules themselves. The marketer's platform sees an anonymous inbound call and rejects it. Anonymous Call Reject is a legitimate feature, older than most of the people now leaning on it. And the presented number is still, in the technical sense, dialable. We would know, diallability is our day job, and a number sitting behind ACR can pass our dips when we present a CLI.
So each individual piece is lawful. The number is presented. The number is dialable. The caller may withhold. The recipient may screen. And yet the one outcome the presentation rule exists to deliver, that you can actually reach the people who rang you, has been quietly engineered away. Worse, it has been engineered away for exactly the people the rule is there to protect, because those most likely to call back with a withheld number are the ones complaining or opting out, and who would rather not hand their number to the very operation that just interrupted their dinner.
The gap is not technical, it is in the spirit
This is not a diallability problem, and we want to be careful about that, because the reflex is always to reach for a technical fix. There isn't one to reach for. The number works, technically. The letter of the rules is satisfied. What is defeated is their object, and that is a harder and more interesting problem than a malformed prefix. A party that is under a legal duty to be reachable is using a legitimate feature to be selectively unreachable, and it has chosen to be unreachable to precisely the people the duty was written for.
What we have done about it
We have put the question to Ofcom, plainly. Not as a formal complaint, because in law there is nothing obvious to complain about, but as a gap between letter and spirit that someone holding the pen should probably look at, whether that turns out to be a line in the CLI Guidance, a tweak to C6, or a quiet word with the ICO, who own the marketing end of this.
We would always rather surface these things and get them closed than leave them sitting there as an unadvertised technique for the scrotes who collect such techniques. Confidence in CLI is built one boring, unglamorous fix at a time. Consider this one more of them, and another action taken by a network that genuinely wants to do something positive for society about the subject matter.