Policy on EMFs in the UK, set by Government, is made up of exposure limits plus certain precautionary measures. Several inputs went in to forming the policy, including scientific advice from the Health Protection Agency and the stakeholder process SAGE. You can read the details of all those by following the links. Here, we set out the policy as it stands now, with particular reference to power lines.
The policy is set out in the Written Ministerial Statement of 2009 (formally, this was the Government's response to SAGE's First Interim Assessment). The policy for power lines has two key planks: compliance with the 1998 ICNIRP exposure guidelines in the terms of the 1999 EU Recommendation, and a precautionary policy called "optimal phasing".
The policy is then formally applied to power lines by National Policy Statement EN-5. In terms of legislation, this applies only in England and Wales, but it sets the principles for the whole of the UK - see more on which bits of policy apply in which bits of the UK
All the practical details needed to apply the policy of compliance with exposure limits is contained in a Code of Practice. This says what land uses the limits apply to, what conditions compliance is assessed for, how accurate the calculations need to be, and so forth.
Part of the system for establishing compliance that the Code of Practice establishes is a list of equipment that inherently complies with the exposure guidelines, and that can be found in this section of this website.
And the practical details of the precautionary policy of optimal phasing are contained in a second Code of Practice.
For low-voltage distribution networks, the agreed precautionary measures are set out in Engineering Recommendation G92 published by the Energy Networks Association. This implements the outcome of SAGE's Second Interim Assessment.