As a driver I can confirm that the main lines between Bristol and London are riddled with wet beds. Some big Some small. Not very often is it needed to impose speed restrictions even if the line speed is 125. From a passenger point of view, ever noticed a bit of a bang from the wheels when hurtling along? This is caused by a train going over a wet bed!
out of our area there is a big one on the line between romley and marple