This paper provides a summary of the sparse literature on the synchrony and diachrony of double modals in dialects of British English, especially varieties of Borders Scots. Double modals are understudied syntactic constructions because they are rare, difficult to describe, and socially restricted. Using the results of recent fieldwork-based acceptability judgment tasks carried out in Hawick, Scotland, this paper examines whether the theoretical literature available on the structure of double modals in dialects of American English can be applied to British English and Scots. I then propose a Speaker's Choice hypothesis whereby double modals can be flexibly analysed as a true modal in first or second position and a recategorized idiosyncratic adverb in the remaining slot of the construction.