British singer Ed Sheeran is convinced laser surgery to remove a birth mark affected his nervous system and gave him a speech impediment. The pop star struggled with a stammer when he was at school, but has learned to control it in recent years. He has now revealed his speech problems started after he underwent a painful procedure to remove a birth mark from his face when he was nine years old. Sheeran tells Britain's Fabulous magazine, "One day they forgot to put anaesthetic on (my face) and it f**ked up my nervous system. It (the stammer) was a problem, but it's kind of gone. It creeps back when I'm under pressure."