Sounds like you’re familiar with CoRE/WebCoRE, you can totally do this, see the guide I posted above on how to setup CoRE/WebCoRE to take action on the unlock event. If you don’t need any advanced features then you can use the stock ST Z-Wave lock device handler and still capture the event and process it.
That would be your call. Since this is a Z-Wave product you’ll need a EU frequency product.
The other alternative is to buy a ZigBee keypad like the Centralite, UEI, Xfinity or IRIS from the US and it should work fine in UK also. They’re pretty cheap. With those you can use the Mitch Pond/Zack device handler if you just want to “capture” the event or if you want to treat it like a lock with user codes you can use the Enhanced Zigbee Keypad Lock device handler and still use it with CoRE/WebCoRE like you would any other lock device.
These ZigBee keypads are pretty cheap, $10 to $20, I don’t know if they’re available in the UK/Eu, you could google it or buy it from eBay and have it shipped to you. e.g