50 years in the computer industry specialising in safety critical systems and cybersecurity. Founder of software engineering company Praxis (now Altran UK). Lots of experience as an expert witness in Europe and Australia. Visiting Professor at universities of Manchester and Aberystwyth (and formerly at Bristol and Oxford). Emeritus Professor of IT and Fellow of Gresham College, London. Fellow of the Royal Academy of Engineering.
I believe strongly that software development is an engineering job and that software engineers should use science-based and mathematical methods for the same reasons that other engineers do: so that they can reason about the properties of their designs and prove the critical properties before putting anyone's safety or security at risk. Testing is important but it can only ever provide very low confidence of safety or security, as computer scientists have been saying since at least 1968.