Re: Sensible suggestion
My preference is for requiring the telcos to automate the process but at much lower fees, say a couple of quid or a fiver for a TPS registered number. Get a call, dial a code when you put the phone down, the fee gets credited to your account and the caller charged with the fee plus the telco's fee. The call came from a different telco? No problem, the charge gets passed to them, they add their own fee and pass it on to the caller. Multiple telcos? It goes on accumulating more handling fees. A telco doesn't know where the call comes from? Tough, they pay the bill and realise they need to keep better records.
Downsides?
There'd be a need to prevent fraud - someone trying to collect a fee on every call whoever it came from so there'd need to be some statistical work to verify problem callers and maybe charge the would-be fraudsters for their trouble.
There'd also be an upfront cost for the telcos putting the mechanism together. In theory their fee covers it, in practice as it would close down the problem PDQ and they'd lose out on their investment. You know what would happen? They'd suddenly find ways to cut down on the problem rather that do that. Not being faced with a mandatory investment they couldn't recover is also good for the bottom line.