The best thing for this sounds like you will need to get a mate to grab the top and bottom of your wheel and rock it while you have a good look underneath at all the steering and suspension components, it is best to put the mini on axle stands to do this!
It would be hard to say with out looking but ball joints don't tend to make knocking noises unless they are really bad, I would first check out the front tie rod bushes then have a look at subframe and engine mounts as they tend to go with alarming regularity.......you can obtain uprated poly bushes from most mini shops, well worth the money!
hope that helps!