Background The aim of this prospective cohort study was to report the performance of existing clinical practice guidelines (CPG) for diagnosis of invasive meningococcal disease (MD) in children presenting with fever and non-blanching rash in the UK. Methods Data were collected prospectively from 37 UK Emergency Departments (ED) between November 2017 and June 2019. Children under 18 years of age presenting with fever and non-blanching rash were included. Invasive meningococcal disease was confirmed by positive culture/quantitative PCR for N. meningitidis from either blood or cerebrospinal fluid. Findings A total of 1329 patients were included in the analysis. Median age was 24 months (interquartile range 12 to 48), 1137(85·6%) underwent blood testing, and 596(44·8%) received parenteral antibiotics. There were 19 cases of MD (1·4%). All CPGs (n=8) demonstrated a sensitivity of 1·00 for the identification of MD. National Institute for Health and Care Excellence (NICE) guidelines CG102 and NG51 demonstrated specificities of 0·00 and 0·01 respectively for the identification of MD. The specificities of the NICE CPGs were significantly lower (p<0.0001) than all other CPGs. The best performing CPGs were the London and Nottingham CPGs with specificities of 0.36 and 0.34 respectively for the identification of MD. Interpretation In the UK invasive meningococcal disease is now a rare cause of non-blanching rashes in children presenting to the ED. Current NICE guidance performs poorly when compared to alternative CPGs.