Ofcom is investigating the ITV talk show Peston on Sunday after actor Miriam Margolyes swore during a live broadcast last month.
Margolyes, best known for playing Professor Sprout in the Harry Potter film series, said “f*ck” when telling a story about US actor Warren Beatty.
The 76-year-old had asked host Robert Peston moments earlier whether she could use a “bad word”, to which Peston agreed.
Conservative MP Sarah Wollaston and Lord Adonis, the other guests on the January 14 show, were left giggling after Peston was forced to apologise.