Petrol hose disconnects from engine on start-up?

Hi i've recently purchased a 1999 1.25cc fiesta zetec which has been running fine for a few weeks until this weekend when I tried to start the engine and nothing happened other than petrol pouring out from underneath the car. After looking under the bonnet, I found that the petrol pipe which attaches to the engine had completely detatched itself. After reconnecting it, the car started first time. However, since then the same thing has happened another 4 times! Does anyone know why this keeps happening, is the pipe snap-on connector faulty needs replacing?