Hi Gav,
could be both but start with the adjustment first. When they are not adjusted properly they hurt your ankle because you are trying to push/ bend it more than it is able to. The adjustment is not easy to get to as it is just inside where the pedal shaft enters the body. There is also the probability the rods/linkages are worn. Without having a method of getting under it I usually find it is easier to drain the oil, remove the battery and tip the mower on its side with the pedal side down so you can see what is going on down there.