Streptococcus pyogenesgenotypeemm1 is a successful, globally distributed epidemic clone that is regarded as inherently virulent. Anemm1 sublineage, M1UK, that produces increased levels of SpeA toxin was associated with increased scarlet fever and invasive infections in England in 2015/2016. Defined by 27 SNPs in the core genome, M1UKis now dominant in England. To more fully characterize M1UK, we undertook comparative transcriptomic and proteomic analyses of M1UKand contemporary non-M1UKemm1 strains (M1global). Just seven genes were differentially expressed by M1UKcompared with contemporary M1globalstrains. In addition tospeA, five genes in the operon that includes glycerol dehydrogenase were upregulated in M1UK(gldA, mipB/talC, pflD, and phosphotransferase system IIC and IIB components), while aquaporin (glpF2) was downregulated. M1UKstrains have a stop codon ingldA. Deletion ofgldAin M1globalabrogated glycerol dehydrogenase activity, and recapitulated upregulation of gene expression within the operon that includesgldA, consistent with a feedback effect. Phylogenetic analysis identified two intermediateemm1 sublineages in England comprising 13/27 (M113SNPs) and 23/27 SNPs (M123SNPs), respectively, that had failed to expand in the population. Proteomic analysis of invasive strains from the four phylogeneticemm1 groups highlighted sublineage-specific changes in carbohydrate metabolism, protein synthesis and protein processing; upregulation of SpeA was not observed in chemically defined medium. In rich broth, however, expression of SpeA was upregulated ~10-fold in both M123SNPsand M1UKsublineages, compared with M113SNPsand M1global. We conclude that stepwise accumulation of SNPs led to the emergence of M1UK. While increased expression of SpeA is a key indicator of M1UKand undoubtedly important, M1UKstrains have outcompeted M123SNPsand otheremmtypes that produce similar or more superantigen toxin. We speculate that an accumulation of adaptive SNPs has contributed to a wider fitness advantage in M1UKon an inherently successfulemm1 streptococcal background.