As has been properly pointed out here, there have been easily identifiable and preventable mistakes made by the plumber.Thank you Darren for you very detailed reply. And to all the replies I've had on here. I'm glad I've posted on here, didn't know whether I'd get completely shot down on. I've got some really consistent replies. Which is great. Thank you again
Just to recap -
He left the filling loop hose connected.
He left the bleed valves on the rads open.
He didn't cap off the radiator valves which is no different to leaving open ends. It doesn't matter they have valves, you still blank off a valve wherever you have one with one side not connected to anything. The only exception to that would be the old Type-B drain cock with the hose connection on but that's not what leaked in your house.