 During a lengthy vacancy in neighbouring Suffolk's diocesan see (while that diocese had no suffragan) from 20 October 2013 to 7 May 2015, he was also the Acting Bishop of St Edmundsbury and Ipswich.He retired on 30 September 2018.A medieval historian, Thomson is a fellow of the Society of Antiquaries of London and the Royal Historical Society as well as an FRSA.