Replaced switch in tailgate but boot latch does not release

Still operates perfectly with remote but not with the new switch.

Any ideas (assuming the switch is actually a good one - it was from Bearmach) what could be at fault?

Not something that I have seen on a FL2, but have seen on many cars.
The wiring loom flexes where the wires go through the rubber conduit to the body, these wires will in the fullness of time break internally. Might be worth pulling the rubber back to have a look.

Also common on drivers and passenger doors.

You could always check the switch operation by simulating the switch operation by shorting out the pins in the plug Tangiers Orange - gone, missing her
Replaced by Ewok what a mistake - now a happy Disco Sport owner

Could be the wiring from the switch. Not much else to go wrong.

The switch is only a simple micro switch so you should be able to test the switch with a multimeter.