Motion Sensing Light Switch Requires Minimum Load of 60W - can I use with LEDs?
This is not really suitable for LEDs. Not only is the wattage too low, but since the switch has no direct neutral connection, it gets its power by trickling a small current through the light. With an incandescent light, the power would be so low that you wouldn’t notice it lighting at all when off. However, with most LEDs, you would probably notice a dim glow or flashing from the light with turned off.
Assuming you have a separate neutral wire at the switch (I have no idea how common this is in the UK), you’ll need to return this switch and get one with a third wire that connects to neutral. Make sure it’s rated for LED lights.