He also was a guest star on the television series Cluedo where he played murder victim Mr. Chapman. He was a celebrity player on Pass the Buck on Christmas Eve 1986. Williams also played Captain Hastings in several BBC Radio 4 adaptations of Agatha Christie novels, starring John Moffatt as Hercule Poirot. Williams has appeared in episodes of Bergerac, Dangerfield, dinnerladies, The Scarlet Pimpernel, Dalziel and Pascoe, Bad Girls, The Inspector Lynley Mysteries, Starhunter 2300, Cutting It, Heartbeat, Family Affairs, Doctors, The Bill, Diamond Geezer 2, Kingdom and First Among Equals. In 1992 Williams starred in the series The Mixer, his co-star was Jeremy Clyde of Chad & Jeremy fame, and appeared as Charles Elliot in the 1997 film The Opium War. Williams has also had recurring roles as Gerald Trigg in Law and Disorder in 1994 and Sir Charles Merrick in Holby City from 2000 to 2003. In 2000, he appeared on BBC Radio's Just a Minute. In 2002 he appeared in the film The Gathering Storm, and has also appeared in the Doctor Who audio drama Nekromanteia. In 2008, he appeared in an episode of the BBC spy series Spooks as bank owner Sir Francis Denham. In 2009, Williams returned to the fictional world of Holby to make a one-off appearance in Casualty as Professor de Silva, the father of junior doctor Toby de Silva. In 2010, he appeared as Lord Godwyn in the television series Merlin in the episode "The Changeling". In 2010, Williams contributed to the CD We Will Remember Them, published by the Royal British Legion, where he read three of the poems. Williams has also written two novels, Talking Oscars and Kill the Lights, and has written several plays. In early November 2007, he performed in Curtain up! Lights up! Cock up! at the Jermyn Street Theatre near Piccadilly Circus in London. Williams has served the Actors' Charitable Trust and Denville Hall for more than 30 years, including 15 years as joint chairman with Angela Thorne. He has donated his time and expertise to the Sir Terence Rattigan Charitable Trust, the King George V Fund for Actors and Actresses, and several other charities. Williams made a guest appearance in the fourth season of the Canadian series Murdoch Mysteries, in 2011. The episode was entitled "Downstairs, Upstairs" in honour of the actor's famous role. Williams has appeared in the audio series Counter-Measures and its follow-up