Women with more than 50 % symptom reduction during PNE test (positive PNE test), is further randomized and allocated 1:1 into one of two arms with 28 participants. One group is allocated to implantation of permanent impulse generator, Interstim II-3058 and the other group is allocated to anal sub mucosal bulking injection of collagen, Permacol. The purpose of this study is to compare the efficacy of SNM to anal bulking injection. The hypothesis is that SNM provides a mean change in improvement in St Marks Incontinence score of more than 4 compared to the anal bulking group. This study is designed as a multicenter single-blinded, randomized controlled trial.