Light Switch Wiring Issue

Congrats on including a picture unprompted! You'd be shocked at how many people don't do that...

I presume you've stuck the wire in the plastic hole and have tightened the screw down only to discover that it doesn't touch the wire, much less hold it tightly. That's a good sign you're attempting to wire it incorrectly.

Back the screw out almost all the way. You'll see the little brass plate dropping down to create a gap. If the screw comes toward the screwdriver and the plate doesn't move, push down/wiggle on the screw until it pops loose. Now, put the wire above the brass plate and tighten the screw. That will pull the plate up and squeeze the wire in tight. This method applies, of course, to all the screw on connections, not just the COM wire.

Your switch should come with some instructions that include torque specs. You really should tighten the screw to the spec torque. If it's too loose, the wire can wiggle loose over time as the entire switch assembly moves every time you flip the switch. That looseness can begin to cause arcing and arcing can cause fires. If you can't find the torque specs on the switch itself or on the packaging/instructions, there should be some "generic" specs available online for your jurisdiction (assuming somewhere in the UK based on the "made in UK" labeling).