Brake pads worn unevenly, is this a caliper issue or something else?

[jacintocollier]

Had my car in for a tyre change and the guy pointed out that my front brake pads are wearing unevenly, one side is almost done while the other still has life left. He said it's probably a sticky caliper but didn't seem confident. I've also noticed the car pulls slightly to one side when braking hard, which I'd been ignoring but now makes sense. I'm looking for expert garage services in DIP since it's close to where I work and I don't want to keep driving on this. Has anyone dealt with uneven pad wear before? Was it the caliper, a slider pin, or something else entirely? And is this something that gets worse quickly or can I drive on it for a bit while I sort out a booking?