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.
The host quipped: “You’ve just got me sacked, which was a public service.”
Please note: Video below contains language which some may find offensive
Today Ofcom said: “We are investigating whether this programme broke our rules on offensive language before the watershed.”
Margolyes, who was born in Oxford to a Jewish family, is also known for her role in the 1993 film The Age of Innocence, for which she won a best supporting actress BAFTA.