Most speech synthesisers and recognisers for English currently use pronunciation lexicons in standard British or American accents, but as use of speech technology grows there will be more demand for the incorporation of regional accents. This paper describes the use of rules to transform existing lexicons of standard British and American pronunciations to a set of regional British and American accents. The paper briefly discusses some features describes of the regional accents in the project, and the framework used for generating pronunciations. Certain theoretical and practical problems are highlighted; for some of these, solutions are suggested, but it is shown that some difficulties cannot be resolved by automatic rules. However, although the method described cannot produce phonetic transcriptions with 100% accuracy, it is more accurate than using letter-to-sound rules, and faster than producing transcriptions by hand.