In 2004 and 2005, Montagu starred in ITV comedy drama Doc Martin as Caroline Bosman, the radio presenter of Radio Portwenn. She co-starred as Lynn, the faithful but put-upon personal assistant, in I'm Alan Partridge and as the huge-breasted, raunchy vicar's wife Sue 2 in Nighty Night. In 2006, she took the leading role of housewife and gang queen Barbara Du Prez in the offbeat comedy series Suburban Shootout. Her other television credits include Mapp and Lucia, Health and Efficiency, Wish Me Luck, Tumbledown, The Harry Enfield Television Show, 2point4 Children, A Touch of Frost, My Life as a Popat, Johnny and the Bomb, Peak Practice, The Queen's Sister, Coogan's Run, Doc Martin, Lead Balloon, Alexei Sayle's Stuff, Skins, Hank Zipzer, M.I. High and The End of the F***ing World.