Confused Brit question - how? That's below min wage, which I thought was national law. I imagine it's a bit lower for youngsters.
Technically you can sue your employer if they wont pay you the difference if you dont end up making enough in tips to end up at or above minimum wage - in practice however, suing your employer is generally not a great way to stay employed
http://www.nolo.com/legal-encyclopedia/michigan-laws-tipped-...
Only way I know round UK min wage is to be self-employed, or one of the fake "self-employed" like some delivery drivers have had to become. Surprised the IR haven't slammed the door on that little scam yet.
That said, it's not uncommon to get at least minimum wage.