It will be the microswitch in the top of the bathroom tap. No pressure switch on that system.

Here's a quick test you can try: open another tap slightly and then open the problem tap. If water flows, it likely means the microswitch is faulty.To fix it, you'll need to lift the tap off its seating, usually held by a big nut underneath. Once it's up, check for any broken wires. Sometimes, it's as easy as re-soldering a wire. You can find replacement microswitches online or watch some repair videos on YouTube for guidance.If you're also thinking about getting new Bathroom Taps, there are plenty of options out there that might work better for you.