Regulation 6 of the Work at Height Regulations 2005 deals with the avoidance of risks from working at height. In summary the regulation requires that where falls cannot be prevented, measures are put in place to minimise the distance and consequence of a fall. In practice this means that the fall distance into a safety net must be as little as is reasonably practicable which will usually be the underside of the structure being worked on, as the greater the fall distance into a net the greater the likelihood of injury.
BS EN 1263-2: 2014 details the maximum permissible fall height into a safety net is 6m from the work position. This means that the maximum nominal fall height from the centre of gravity of a person is 7m.
It should be noted that for safety nets less than 35m2 in total area, or a side length less than 5m the maximum height an operative is allowed to work above a net is 2m as there is insufficient fabric area to absorb the energy of falls from a greater height.