st220 water leak need help

[scat257]

I have a 52 plate mondeo st220,car running at normal temp but sprung a leak,this was coming from a small pipe that comes off the thermostat and goes to another pipe on the engine this is just belwo the water pump,pipe is about 2 inchs in dia and about 4 inchs long,the leak was at the engine end not thermostat,so i changed the pipe thinking it was split which it was not also changed the thermostat in case it wasnt working propley and cause excess presure as it only leaked when hot.
none of this solved the problem and still it leaks,so from looking i beleive its leaking from the pipe that this small rubber hose connects to as i am sure its plastic can anyone tell me what this is and where it goes and even better how i can fix this annoying problem.i cant see any other pipes or places this is leaking.
stuart