JudeL, "Oh, Brother", actually starred Derek Nimmo, rather than Derek Jacobi. (Sir) Derek Jacobi has not (to my knowledge) appeared in any comedy series, although he has a very dry sense of humour, which he displays when appearing on panel game shows.

Derek Nimmo appeared as another ineffectual cleric (C of E, this time), in a series which I haven't seen for many years; "All gas and gaiters".