This is the latest from UK Athletics:
From 1 April 2016 a new rule regarding the wearing of head phones in road races was introduced into the 2016-2018 edition of the UKA Rules of Competition.
“The wearing of headphones, or similar devices, (other than those medically prescribed), is not permitted in races on any single carriageway road that is not wholly closed to traffic.
This restriction does not apply to races held on dual carriageways provided that there are clear, structured separations between the separate carriageways. Competition Providers of races held entirely on roads closed to traffic may apply this condition where appropriate to local circumstances.”
Race Directors may apply the condition to any race where they consider the wearing of headphones to be a hazard – including, for example, where runners must be able to hear marshals’ instructions or on a lap course, and UKA will support the race director where that local condition is applied.
Enforcement of this rule is a matter for the race director and referee and disqualification of runners who choose to ignore it is an option.