Ashton started his professional career at Worcester Repertory theatre, playing roles such as Marco in A View from the Bridge, Jerry in Two for the Seesaw, Harold Gorringe in Black Comedy, and Charlie in Staircase.
Other main roles include Lieutenant Wickham in The Voyage of Charles Darwin (1978); Mr. Fraser in the BBC Scotland produced drama Maggie (1981–1982); Doctor MacDuff in Brass, a social comedy series, set in 1930s Northern England (1982–1984 & 1990); Major Lennox in Sharpe’s Eagle (1993); Major Roddy Maclean in Hamish Macbeth[1] (1995–97); Harold Xavier in Monarch of the Glen (2000); Alex Gemmell in Glasgow Kiss (2000) and Professor MacManus in Vital Signs (2006).
He has also had featured roles in New Tricks (2008); Waking the Dead (2002); Waterfront Beat (1991); All Creatures Great and Small (1990); The Bill (1989); Ever Decreasing Circles (1986); Doctor Who (as Kendron in the 1985 story Timelash); Coronation Street (1985); and Juliet Bravo (1980 - Series 1, ep.6 'The Runner').
His monologue Stations (1988), broadcast as part of the BBC’s Play for One series, provided actor Andrew Keir with "a tour de force solo role" according to The Independent newspaper.
The dramas star Brian Cox as McLevy, Siobhan Redmond as Jean Brash, Michael Perceval-Maxwell as Mulholland, and Ashton himself as Lieutenant Roach.