Turned away at airport for not having a visa

My friend was due to fly from Gatwick last night but was tuned away as he did not have a visa. He is originaly from Ireland and has a British Subject passport. He goes to Icmeler a 3 times a year and just came back from his last holiday in June with no problems. He was told that the law had changed and that he had to get a visa before he could fly. He also explained that he still had time left on his visa from June,but was told that when you leave Turkey your visa is not valid for re-entry. Can anyone give any advice on this as we have tried to ask advice from various travel agents but they won't comit to anything. 
