Hi well it's one of two things, the switch itself or the well known hatch wiring issue.
First try removing the whole silver trim and test the action of the switch, there's only 3 wires two for the number plate lights(one of the two is common to the lights and boot switch-earth wire) and the remaining one, when the boot switch is pressed it earth's the boot release switch sending a signal to the solenoid. Check using a meter with the bulbs removed, ours I was faulty I could not find a fault but once replaced it generally works sometimes requiring a hard knock on the top of the silver trim. If the switch is confirmed as ok it's the hatch wiring not hard to fix but time consuming for someone confident in repairing it.