Posted By Sean Fraser Stewart, In the past Standards were not legally enforceable directly, although they could be cited as being the accepted industry norm for certain applications that would be considered persuasive to the court if someone was found not to have applied them, but that didn't mean they must be used IF there was an equivalent that could be proven to meet or exceed the standard. Indeed, most BSI Standards have disclaimers on them that state "compliance with a British Standard does not itself confer immunity from legal obligations". However, this general understanding of the legal connection between statute and standard is now confused by the introduction of the CE marking regime. Certain regulations now insist that new equipment (pressure vessels, supply of machinery) must be CE marked - the mark itself is meant to represent that the item meets the relevant European and harmonised Standards. So the link has been stregthened through European directive, something that UK law had been reticent to do in the past. Example - hard hats, as PPE, must now be CE marked. Anyone selling goods in the EU must make sure their items will comply with the relevant safety standards and mark their products accordingly. Failure to do so will be an offence not only by the seller but also by any purchaser, as the Regs apply to both. Ignorance is no defence. So the answer is two-fold. If the goods are covered by recent Regulation then Standards are likely to apply through the CE marking scheme (note that specific Standards are not referenced in the Regulations themselves) and are considered mandatory in that respect. If the goods do not come under such legislation, then application of Standards remains voluntary. However, a failure to apply a widely recognised standard might be prejudicial in any court case, especially if they are national or international standards as opposed to industry standards, unless there is an excellent justification against their use. I hope that is a simple enough explanation as requested, to what was an intersting question.