  UK researchers have made major contributions to the technical ideas
underpinning formal approaches to the specification and development of computer
systems. Perhaps as a consequence of this, some of the significant attempts to
deploy theoretical ideas into practical environments have taken place in the
UK. The authors of this paper have been involved in formal methods for many
years and both have tracked a significant proportion of the whole story. This
paper both lists key ideas and indicates where attempts were made to use the
ideas in practice. Not all of these deployment stories have been a complete
success and an attempt is made to tease out lessons that influence the
probability of long-term impact.
