The American Sniper star appeared on The Graham Norton Show, which aired in the U.K. on Friday (30Oct15), alongside her Burnt co-star Bradley Cooper, but she was not sporting the distinctive red flower.

Host Graham, Bradley and fellow guests Dame Maggie Smith and actor Alex Jennings all wore a poppy, which is traditionally sported by Brits as a mark of respect for the nation's war dead ahead of Remembrance Day (11Nov).

Sienna's poppy-less appearance on TV was criticised by former British defence minister Sir Gerald Howarth, who said, "There should be no excuse for not wearing one so we can honour the war dead."

Some users also slammed the actress, including one who wrote, "Why is Sienna Miller not wearing a Poppy? Has she refused? If yes why is she allowed on the show? Disrespectful c**."

BBC bosses said guests decide whether they want to wear a poppy, and a source told editors at British newspaper The Sun on Sunday that the actress wanted to wear one onscreen but its pin was snagging on her dress so she had to remove it.

A representative for Sienna has yet to comment on the reports.