[3] While with them he toured North and South America, Australia, New Zealand, Israel, Lebanon, Russia, Poland and the Far East,[1] and performed in Twelfth Night opposite Vivien Leigh.

[3] During the 1970s and 1980s he appeared in Doctor at Large, War and Peace (a memorable performance as Mikhail Kutuzov), Crown Court, Last of the Summer Wine, Ripping Yarns (Murder at Moorstone's Manor), Upstairs, Downstairs, Poldark (1975), Fall of Eagles (as Russian Prime Minister Pyotr Stolypin), The Sweeney and Emmerdale Farm.

[1] Middlemass followed this up with a notable performance in the BBC Television Shakespeare production as The Fool to Michael Hordern's King Lear, as Henry Baker in The Blue Carbuncle episode of The Adventures of Sherlock Holmes in 1984 and Brezhnev in Tom Stoppard's Squaring the Circle.

[1] Middlemass's voice work includes the albums and radio plays: Carol and the Advent Calendar, The Hitchhiker's Guide to the Galaxy[17] and Hordes of the Things.

Middlemass also appeared in films, including roles in Otley (1968), Frankenstein Must Be Destroyed (1969), Say Hello to Yesterday (1970), Madame Sin (1972), Barry Lyndon (1975), The Island (1980), as the voice of the Caterpillar in Dreamchild (1985), and Mrs Caldicot's Cabbage War (2002).

[21] Middlemass joined the Royal Shakespeare Company in 1984 and his Shakespearean roles included Friar Lawrence in Romeo and Juliet, Quince in A Midsummer Night's Dream and Holofernes in Love's Labour's Lost.

[24] Middlemass never married, and for forty years he had a room in the house of his close friend, actor Geoffrey Toone, who died in 2005 after spending some time resident at Denville Hall.