I disagree Steve. Yes it's true that you will typically have only two conductors in most one way switches in the UK. It is perfectly acceptable, however, to have a neutral running to the switch, providing it has been properly terminated (dead end terminated if necessary). When quoting for a re-wire, I offer a service in which I make switches ready for smart home features. I run three core cable (plus earth) to the switches which provide conductors for all four (Line, Switched Line, Neutral & Earth). This only costs an extra £40 or so in cable with no additional labour charge. Also, on ALL rewires, I install deep 35mm back boxes on all switches and sockets to allow for the increased depth of some smart/decorative wall plates (such as the Sonoff Touch). Of course, this service often leads to follow up work installing smart home systems.
I admit I may be out of date on 17th Regs - but I would suggest that the percentage of home wired like this must be absolutely tiny sadly.
The two wires you have in your existing UK wall socket are the live feed in, and the switched feed which goes to the lamp. In a UK wall plate the neutral is NOT present - in fact it is not allowed to be due to the risk of a short. You therefore have no neutral available to power a wall switch assuming it needs mains power, so probably cannot use it.