This happened today with calls spoofed to various 020 xxx numbers. The first just went dead immediately. The second died after a few seconds, but I heard rustling in the background.
The third alslo had the rustling sound......... so I gave a loud blast on the whistle.



Not had another, but I lie in wait.



1471 says the number is 01235874537, Abingdon area, but it is not recognised.