There was a leak from the radiator (squirting from one spot)

My Fiance has a Peugeot 106 1.5D. I've noticed recently that the coolant level drops quite frequently after topping up and running the engine. Then last night after we stopped and got out of the car there was a leak from the radiator (squirting from one spot). Does this mean a new radiator and would you be able to tell if this was the only problem in the cooling system.

P.S. The leak only occurs when the pressure is built in the system. After the pressure is released the leak stops