Well personally I'd recommend shortening the chain and checking the chain line first of all, as they need doing anyway, if that doesn't sort it I'd take it off and send it back to tarty. The general concensus is that those freewheels are the dogs bollocks, you could just have a funny one.
Some people say freewheels need to bed in, I disagree. There's nothing rubber of anything that forms itself in there, it's all hardened steel, so you can be sure that it might wear in over time, but if it's skipping from new and there's no grease in there anyway, just oil, then there's something wrong with it.