Ofcom are consulting on proposals to include a specific condition in Wireless Telegraphy Act licences requiring licensees to comply with the relevant levels from the ICNIRP Guidelines (PDF, very technical).
This condition would apply to all equipment which can transmit at powers above 10 Watts (including, for example, the licences of mobile phone companies, TV and radio broadcasters, most point-to-point microwave links, and Amateur Radio)
Amateur Radio licences already contain conditions requiring safety precautions against radio frequency (RF) radiation to be taken in line with Public Health England (PHE) recommendations and that the radio amateur syllabus covers health aspects of electromagnetic fields and also refers to PHE and the ICNIRP Guidelines but may have to be amended to give effect to the proposals.
To get an idea of how this could affect an Amateur Radio station I’ve uploaded a tool to calculate the field strengths for a variety of antenna types and output powers.
The tool allows you to explore your antenna setup (there are lots of predefined antennas and the ability to input the parameters for your antenna if it’s not included) and see what sort of separation you’d have to achieve.
Basically you would need to keep the public 1m away from an dipole fed with 100W, easy enough unless you’re running it along a fence, higher powers and more directional antennas produce higher EMF levels within their transmit lobes so you would want to keep the public up to about 5m away (easy enough if at the top of a 20m tower).