There may not be such a regulation in the UK or EU, unless it comes under NATO requirements, which would be military.
It is good practice however, even with LOTO protocols, to always have two people around, remove all rings, watches, etc., and use only one hand actually near wiring or grounding whenever possible.
If this is for a company's procedures, you can always include the requirements as good practice, if you are unable to find any other regs or laws.
Hope this helps.
Hershal