IIT IS NOT ILLEGAL! Do not get misinformed, this is a standard dentist rant because we offer it so much cheaper as we don't charge for time in our professional chair. The law was changed in Oct 2012 to clarify this issue.
cosmetic technicians can use 0.1% peroxide whilst dentists can use 6%. See the link below. http://www.legislation.gov.uk/uksi/2012/2263/made
We were wisely warned during training that dentists will regularly attack you and the GDC is not much better, it's all down to money. I always keep a copy of the law with me when working, together with full chemical reports of the products I use and my liability insurance. That generally sends any dentists that fancy a pop on their way rapidly.
By the way, I trained with Hollywood Smiles, excellent, great follow up, great price and they are manufacturing and supplying their own products to most of the other training companies anyway.