It has been more than 20 years since the publication of Jean Paton’s The Liverwort Flora of the British Isles. The main objective of this supplement is to introduce species that had been found and added to the British list since the publication of the flora and to update other species and text. The new taxa included are detailed in the same sequence and illustrated as in the flora. A Supplement to The Liverwort Flora of the British Isles offers the opportunity to fill in other gaps in the British liverwort list, to add information on some of the selected species, to correct errors in the flora, and to provide a chance to use the comparative comprehensive bibliography.