I thought that and I removed the receiver and cleaned it out because I thought there might be some stones or dirt or something blocking it, but it seems to be fine.

From reading around a bit I have a feeling it might be a broken ground wire in the boot wiring loom (as per this video: https://youtu.be/SezYJ5uDJoM )

Will take a look at that tomorrow. Hope that’s not the case as anything to do with wiring/soldering, etc. is out of my comfort zone!