That link you included is well worth reading through. I suspect that a lot of business owners have only a sketchy idea of their statutory obligations to "deemed workers," which term has a very wide definition. On a particular point I will pretty much guarantee that not a single business in the industry could pass the "wages" audit which can be demanded by Workers Comp insurers. "Wages" has a very broad definition and access to information cannot be withheld, notably an audit can get past any income splitting and sub-contracting arrangements.
Probably observed mostly in the breach, but if councils wanted to get tough, creative use of the health and safety and wages legislation might be far more effective than their occasional use of private detectives.