I phoned the number back, to hear a recorded message that the call was “on behalf of a charity ...”

I hung up. These unsolicited calls should be prevented. Who wants to donate to aN unsolicited “cold phone call“? One can never be certain how legit the caller is.

There’s much better, safer ways to make donations to charities!

Caller: Charity

Message if you return the call is "you may have supported one of our charities before" - so suspect it is one of these call centres that fundraises for multiple charities but only passes on a fraction of the donations. Recommend you avoid it and deal direct with your preferred charity.

didn't identify, sounded like the usual bogus charity call