DNA analysis and mutation identification is useful for the diagnosis of familial hypercholesterolaemia (FH), particularly in the young and in other situations where clinical diagnosis may be difficult, and enables unambiguous identification of at‐risk relatives. Mutation screening of the whole of the three FH‐causing genes is costly and time consuming. We have tested the specificity and sensitivity of a recently developed multiplex amplification refractory mutation system assay of 11 low‐density lipoprotein receptor gene (LDLR) mutations, one APOB (p.R3527Q) and one PCSK9 (p.D374Y) mutation in 400 patients attending 10 UK lipid clinics. The kit detected a mutation in 54 (14%) patients, and a complete screen of the LDLR gene using single‐stranded conformation polymorphism/denaturing high performance liquid chromatography identified 59 different mutations (11 novel) in an additional 87 patients, for an overall detection rate of 35%. The kit correctly identified 38% of all detected mutations by the full screen, with no false‐positive or false‐negative results. In the patients with a clinical diagnosis of definite FH, the overall detection rate was higher (54/110 = 49%), with the kit detecting 52% of the full‐screen mutations. Results can be obtained within a week of sample receipt, and the high detection rate and good specificity make this a useful initial DNA diagnostic test for UK patients.