I sat in a taxi once when he received a call purporting to be from HMRC about his taxes. I think I managed to intervene forcefully enough to make him understand that no, HRMC would not ask him to call back via Vyber or whatever, and no they'd never ask him to send money without actually sending a letter.

But this only after he had called them back while I was listening in - that was when I interrupted.

A big problem is so many people have situations ongoing with HMRC (as did that taxi driver) that it seems plausible to them, because it's all confusing anyway, so make the call a bit scary and people seem to shut off all critical senses.

I stressed to him that if he got any calls like that again and was unsure, to always hang up and call the numbers on the HMRC website, and hopefully he got the point...