Researchers found nine out of 10 sunbeds in England exposed users to more UV radiation than is deemed safe by European standards.
They found the risk of skin cancer from exposure to some tanning beds was six times higher than for the Mediterranean sun at noon.
Researchers said the situation was 'unacceptable' and urged stricter controls.
A meta-analysis had found adults were at 75% greater risk of melanoma by using indoor tanning during their teenage years.
As a consequence, the EU declared in 2006 that UV tanning equipment should not exceed an erythema-weighted irradiance level of 0.3Wm-2, a measure of UV output. The UK and other EU countries agreed to implement the measure from 1 April 2009 for all new tanning devices.
To examine the emissions from existing sunbeds, researchers at the University of Dundee measured UV emissions of 402 units in England between October 2010 and February 2011.
The authors found that emissions varied from 0.1 to 1.32Wm-2, with an average of 0.56Wm-2. Just 10% of beds were within recommended safe levels.
After applying a weighting factor for skin cancer risk, they found some beds exceeded 2.52Wm-2, six times higher UV levels than the midday Mediterranean sun at 0.43Wm-2.
The authors said European safety standards designed to protect the public were being 'largely ignored' by the sunbed industry.
Tierney P, Ferguson J, Ibbotson S et al. Br J Dermatol 2013; 168: 602-8