Possible Afro-Asiatic Substratum
The concept of the Insular Celtic languages being descended from Hebrew was part of Medieval superstition, but the hypothesis that they had features from an Afro-Asiatic substratum (Iberian and Berber languages) was first proposed by John Morris-Jones in 1900. Some well-known linguists have been adherents such as Julius Pokorny, Heinrich Wagner, and Orin Gensler. There has been further work on the theory by Shisha-Halevy and Theo Vennemann.
However, the theory has been strongly criticised by Graham Isaac and by Kim McCone. Isaac considers the twenty points identified by Gensler as trivial, dependencies or vacuous. Thus he considers the theory to be not just unproven but wrong.
Read more about this topic: Insular Celtic Languages