This study is based on the British National Corpus (BNC) and also takes data from the London-Lund Corpus (LLC) into account. It shows that the so-called filled pauses er/uh and erm/um are sociolinguistic markers that differentiate between registers of English and along gender, age and socio-economic class. Men, older people and educated speakers use more fillers than women, younger speakers and less educated speakers. Nasalization is used more often by women, younger speakers and more educated speakers. These sociolinguistic factors can probably partly explain the fact that the use of fillers is higher in the LLC and the context-governed sample of the BNC than in the demographic sample of the BNC. It is argued that a more positive view should be taken of fillers as planning signals, or planners, and that their functions should be submitted to careful discourse analytic study. Their recognition as words will facilitate such an undertaking.