Many race organisers are following the new England Athletics rules of competition and banning the use of headphones on safety grounds. The logic is that you are far less likely to hear traffic, instructions from marshals and warnings from other runners.
The detail of these new rules can be found here. Search the .PDF for rule 240. At the time this FAQ was last updated (Feb 2017) the rule said
“RULE 240 S 5 UKA SUPPLEMENT – HEADPHONES
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.”
The club does not ban the use of headphones at training sessions but we do encourage you to talk to one another and headphones get in the way of that so we prefer it if you didn’t wear them when training with us.
When you are on your own then it is your choice but for safety we think there are good grounds for not using them if you are running in areas where you may encounter cycles or vehicles.