Arguments about the socio-political significance of the informalisation of English have been central to the critical study of language in society since the 1980s. This paper demonstrates that informalisation was also a key concern of ordinary users of British English in the 1980s. Correspondents in the British Mass Observation Project articulated judgements of informalisation that were in many ways continuous with those of academic linguists. The paper argues that such critical arguments about language were part of a ‘structure of feeling’ (Raymond Williams) of late twentieth-century Britain. This suggests a rethinking of ordinary language users’ relations to their linguistic experience, not as unthinkingly ‘prescriptivist’, nor as merely ‘common-sensical’, but as exhibiting a nuance which academic linguists would do well to engage with more fully. The paper makes the case for the use of social-historical archives in investigations of metalanguage, as a means by which the social significance of language can be better understood.