Hoping someone can ID this bird call!

Recorded in rural South Wales, UK, last September, nobody I've played it to can tell what it is (and Merlin didn't know either)

https://drive.google.com/file/d/1TwEW5eprcyu8PtiOfxdwc_8hdDLn25wV/view?usp=drivesdk

(Apologies for the Drive link but I couldn't find an easy way to share audio files on here directly)