You in the UK aren't alone; the plague of roundabouts has finally penetrated even to the west coast of the US; we've had speed bumps for decades, so I guess sharing the pain is the order of the day.
I'd suspect a ball joint, but look at the bushings, too.
Checking ball joints isn't easy, but with the weight of the car on the wheels, pry at the ball joint with a pry bar; if it moves much at all, it's time for a new one.
--
Jim McDonald