From the Governments own announcement of the new regulations last October:
<These changes will require employers to pass all tips, gratuities, and service charges on to workers, without deductions.
From today, if an employer breaks the law and retains tips, a worker will be able to bring a claim to an employment tribunal. >
So, it doesn't matter whether it's called tips or service charges, 100% of that amount is supposed to go to the workers not the business revenues. I don't know how they will enforce it though.