Ash joined the Department of Electronic and Electrical Engineering at University College in 1963, became a full professor in 1967. He was appointed Head of Department, and holder of the Pender Chair, in 1980. He was elected a Fellow of the Royal Society on 17 March 1977, and was awarded its Clifford Paterson medal shortly afterwards. He was elected a Fellow of the Royal Academy of Engineering in 1978. He worked on problems in physical electronics, ultrasonic signal processing and imaging. He won the Marconi Prize in 1984 "for leadership in electronic technology, including surface acoustic wave devices and optical fibre communications". He won the Royal Society Royal Medal in 1986, in "recognition of his outstanding researches on acoustic microscopy leading to wholly new techniques and substantial improvements in resolution of acoustic microscopes". He also won the Institution of Electrical Engineers' Faraday Medal. He is also a Senior Member and Life Fellow of the Institute of Electrical and Electronics Engineers (an organisation based in the United States that complements the IET).