vw t4 suspension knocking at front when cornering????

I have what is probably a simple problem but i have no idea what it is. When cornering the drivers side wheel/suspension makes a single knocking sound as though something is moving to one side, then when i make a turn the other way the same thing happens. Its done a few miles so i guess something has worn out... any ideas?

VW transporter 1990 swb petrol