For over 50 years I have worked in the herbarium at Cambridge University on the British and European floras. I have collected about 30,000 numbers consisting of some 50,000 specimens from most parts of the British Isles and made many visits to Continental Europe. Particular attention has been given to most critical genera: Cerastium, Conyza, Crepis, Dactylorhiza, Euphrasia, Fumaria, Hieracium, Limonium, Pilosella, Prunus, Rhinanthus, Salicornia, Salix, Scleranthus, Sorbus and Ulmus; and in helping friends in various ways I have considered the taxonomy of Alchemilla, Batrachian Ranunculi, Chenopodium, Potamogeton, Rubus and Taraxacum. I have also spent much time studying ecotypic and geographical variation, in particular a comparison of those variants which occur on the coasts in dunes, shingle and salt-marsh with those growing as arable weeds, and those in mountains. Special attention has also been given to trees and shrubs.
It has long been my wish to publish this information in a critical flora of Great Britain and Ireland. In the 1970s a group of us tried to get a grant to carry this out, but we were unsuccessful. Clive Stace then started work on his New Flora of the British Isles, which was first published in 1991, with a second edition in 1997. In it he gives only abbreviated descriptions and omits most of the species in the large apomictic genera and many of the infraspecific variants.