AngelEye's informal American English expressions would be used in exactly the same way in British English. (It is pleasant to be able to write this - forer@s spend much energy pointing out the few differences.)
I would not use: "His legs must be paining him." I would use: "His legs must be aching."
"To pain" as a verb is almost always used in the sense of to irritate, to annoy or to cause grief.