Spewing out coolant!

My P38 2000 4.6 has started to spew out coolant all at once - usually when i switch off the engine.........it leaves a significant puddle! It forms at the front on the driver's side - could be wrong but it does not seem to be coming from the radiator - I havn't had time to have a good look. Any thoughts would be much appreciated. It is heading for the garage on Monday for a couple of fixes so I suppose another job will be added to the list.

Expansion cap not down tight or faulty if you are lucky, or HGF slipped liners if not. Gas test on the coolant needed.