I have a 54plate 1.8 focus and it has a steering problem, that i hope someone can point me in the right direction.

When ever I turn the steering to the left, just off centre I feel some resistance, then a clunk. which often results in the car pulling to the left sharply becasue of how hard i have to turn to make it turn left. It does this most times now and is becoming worrying that it will eventually fail.

Can anyone point me in the right direction of what i need to do so i can resolve this problem.