Hello, what tool do I need to unscrew the plastic boot liner?
It looks like some sort of start shaped torque screw but I've no idea of the name.

I need to get access to my rear-windscreen washer tube once it's in the boot area as it split in the winter and I traced the leak back to here.

I've checked ePER but no mention of tools other than the replacement wheel tools.

5 mm allen key

Rear washer jet/pipe you get to by removing the 2 rubber grommets at the high level brake light not the boot liner (do you mean tailgate trim?)

If you mean the plastic trim along the bottom lip of the boot its a torx 30 but washer tube does not run along here either.

Boot liner is held in by 2 pozi screws and a t30 torx bit