"If a caller really wants to speak to you, they will (or should) leave a message."
That's slightly based on a presumption that there's an answer machine.
At times I have realised that cold-callers can be allocated a block of numbers, and you can block the whole lot in one go.
Other methods
Answer, but don't speak and leave the line open until the call is terminated. Sometimes misconfigured automated calling systems can leave the line open for a very long time. Like over an hour.
If there's a scammy real-world person at the other end then play them for the fools they are.
Ofcom will and do accept reports of scammy phone calls (or calls presenting a non-standard CLI or operators not adhering to accepted/defined standards/laws).
Ganeral rule: financial downturn = upturn in scams/cold-calls. And there are other factors that influence prevalences of scams.
I have (in the past) been known to pick up a cold-call, listen to the scammy (lie) line, terminate the call and then call the presented CLI number back. Only to listen to a rather different scammy line. And that would be on a number issued as part of a block of numbers. Hence some of my other observations.
Perhaps landlines are going to be extremely untrustable in the future.
