The occurrence of sting jets has been linked to observed slantwise circulations near or within the frontal fracture region. Furthermore, these circulations have been associated to the presence and subsequent release of conditional symmetric instability (CSI). The purpose of this work is to understand and quantify the role of CSI in the development of sting jets. The analysis presented in this study is based on various diagnostics for CSI. Computations of moist potential vorticity (MPV) show that regions of negative MPV are indeed related to the initiation of sting jets. We also discuss the use of slantwise convective available potential energy (SCAPE) and downdraft SCAPE in the study of these phenomena. We illustrate these ideas through a case study, namely the analysis of a storm that occurred during the first hours of 26/02/2002 over the UK. This storm was characterized by very strong surface winds over localized regions of Wales and the north of England. We also present some ideas regarding the use of these diagnostics in the development of a climatology of sting jets.