Can't help but send th ebill to the council!
And why would that be, he says when he drives over a pothole it knocks, that would suggest a problem with lower arm, as the op says bush, or ball joint.
Its not just pot holes that it would knock on, no doubt if he drove over a speed bump, it would knock.
I drive over pot holes all day and night, very hard to avoid them the state the roads are in, and its not damaged my car.
Lower arm bushes or ball joints do just fail, ball joints all it takes is a little split in rubber, water gets in and and mixes with grease washes grease out and the ball joint is goosed, and the ball joint just rattles around in it seating. = knocking.