I’d agree with Ian. Of course, it is possible that your service provider doesn’t offer that facility.
Asterisk can detect calling party clearing on an analogue line either because the network temporarily removes the battery voltage, or, as a less preferred option, the network puts a tone on the line. If they do neither, or you don’t configure for the correct one, there is no way that Asterisk can tell the call has been cleared.
If they put a tone on the line, you should be able to hear this on the recording. I’m not sure what sorts of tone Asterisk can detect.
BT in the UK can use one or more of three methods, two as above, and one which Asterisk can’t detect, which is simply to make the line silent, See section 7.2 of sinet.bt.com/351v4p5.pdf