 Mustow was appointed a Commander of the Order of the British Empire in the 1995 New Year Honours for services to civil engineering, at which point he was a non-executive director of WS Atkins.Mustow ran the "S and S Mustow Trust" with his wife Sigrid between 21 October 1970 and 15 February 2017.The charity made grants to educational, religious and poverty relief charities and individuals and was defined as a Protestant Christian organisation.