Yes, that’s a 9V battery compartment.
Ok, I’ve just realised how blonde I’ve been: the volume/tone and pick-up selector knobs were stopping the control panel from lifting off. They just pull off and then all is fine.
Unfortunately, the switch and pot are soldered into the PCB board, which would make it a bit trickier to replace them. I’m pretty happy with soldering wires but I’ve never tackled a PCB board.
It’s all good now, thanks.
(Solution/problem above ↑)