Grenville was a founder member of the SDP in 1981 but it was his involvement in the community that led Grenville in 1987 to stand as a City Councillor. He was elected to the Durham City Council for the Framwelgate ward, which, after boundary changes in 2003, became the Crossgate & Framwelgate ward. When the Liberal Democrats took control of the City Council in 2003 he was elected as Deputy Leader of the Council with Cabinet posts in Leisure and Environment and later Culture and Economic Development. In 2008 he was elected as the Right Worshipful the Mayor of the City of Durham and was made an Alderman of the City in 2009.

As part of his Mayoral duties Grenville was honoured to present Sir Bobby Robson with the Freedom of Durham (Photograph Journal Newspaper).  The same year he also awarded Freedoms to the international acclaimed sculptor, Dr. Fenwick Lawson, and to the author and Chancellor of Durham University, Dr. Bill Bryson.

Click here to watch the video on the service https://www.gettyimages.ie/detail/video/sir-bobby-robson-receives-freedom-of-durham-holland-news-footage/827938290

https://www.gettyimages.ie/detail/video/sir-bobby-robson-receives-freedom-of-durham-more-shots-of-news-footage/827929430

In 2008 Grenville and Nigel were selected to stand for the new unitary council. The Labour Government’s decision to close all District Councils in CountyDurham and instigate a single unitary authority brought about major changes. The Crossgate and Framwelgate ward formed part of the Nevilles Cross Division. In May of that year both Grenville and Nigel were elected to represent this division in the new County Council, and they were returned in May 2013.

In 2017, Grenville and Nigel both decided to retire from the County Council, but not before helping the Lib Dems in Liz Brown and Elizabeth Scott to retain the Lib Dems position in Neville’s Cross.  Grenville’s political retirement though lasted less than 24 hours as he was elected by the Framwellgate Moore voters to serve on their Parish Council, and provide much sort after experience in particular on planning, to the Lib Dem run Parish Council.