Wireless Body Area Network (BAN) is a mainstream technology for numerous application fields (medicine, security, sport science.. .) and precise determination of wireless sensors' positions responses to the great needs in many applications. In addition, Ultra Wide Band (UWB) radio is an attractive technology to achieve the centimeter-level distance measurements. However, the aggregation of the distance information remains a challenge and this paper presents a cutting-edge method for performing the accurate localization in wireless BAN. To this aim, by fully exploiting its unique features, a novel Cooperative-cum-Constrained Maximum Likelihood (CCML) localization algorithm is developed. Simulation results and UWB-based platform validation show absolute agreement with theoretical prediction and improvement over previous studies by Hamie et al and Mekonnen et al.