The majority of scholarly opinion has long held that Celtic influence on English has been minimal on all levels of language. This is usually put down to the socially and politically inferior status of the Celts vis-à-vis their Anglo-Saxon conquerors, which then explains the small number of Celtic loanwords in English. This article joins the voice of those scholars who have challenged the prevailing view and called for a fresh examination of the ‘Celtic Hypothesis’. It is argued, first, that the nature of the contact situation was such that linguistic influences from Celtic on English were inevitable. Secondly, the paucity of Celtic loanwords in English does not constitute evidence against contact effects at other levels of language but is the expected development. Thirdly, many features of English grammar have characteristics that cannot be satisfactorily explained as independent developments. Fourthly, the modern-era ‘Celtic Englishes’ provide yet another source of indirect evidence supporting the Celtic Hypothesis.