[ITSv40]

Are you sure it is coming out of the block. Most likely cause is a split hose somewhere. Bottom hose clip on the radiator rusts an eventually gives way - not good if you are in the outside lane of a motorway when that happens. If not a hose could be the waterpump but these do not normally go all of a sudden. If it is the waterpump fairly straightforward to do, you will need a new timing belt though as that has to come off to get to the pump. At least it appears the problem started when the engine was only ticking over or gently cruising, so no lasting harm should be done.

It is a Fcuk it feeling though, but most likely it could be worse than it actually is.