Bafta has said it is taking a security breach during Sunday night’s best film speech “very seriously”.
A man, thought to be a YouTuber, was seen standing in the background as Christopher Nolan and Emma Thomas accepted their award for Oppenheimer.
The gate-crasher did not make any notable gestures or attempt to speak.
A Bafta spokesman said: “A social media prankster was removed by security last night after joining the winners of the final award on stage.
“We are taking this very seriously, and don’t wish to grant him any publicity by commenting further.”
Bafta did not name the individual, who has not yet posted about the stunt on YouTube or TikTok.
However, Variety reports it is not the first time the YouTuber has infiltrated a major awards ceremony.
He is previously thought to have gate-crashed events including the Brits, the Mobos and the Ballon d’Or football awards in France.
At the Baftas, the Oppenheimer team were sitting together to the right of the stage before Nolan, Thomas, actor Cillian Murphy and producer Charles Roven got up to collect the trophy.
The prankster, dressed in a black suit and hat, then appeared from the opposite side of the audience and ran up the stairs to join them.
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Oppenheimer producer Thomas opened her speech by urging other cast members to join her, saying: “Where are you? Come on, all of you!”
Her invitation meant few people in the auditorium, or watching at home, suspected the man of being a gatecrasher.
He stood next to actor Cillian Murphy, who had earlier won best actor for his portrayal of theoretical physicist J Robert Oppenheimer.
When Thomas finished speaking, the crowd began to clap. The man then appeared to tuck something under his arm and also began clapping before walking off stage with her, Nolan, Roven and Murphy.
Michael J Fox, who presented the award, and ceremony host David Tennant, were also on the stage at the time.
However, none of those on stage appeared to interact with or react to the interloper.
Oppenheimer was the big winner at the awards, which were broadcast on BBC One, taking home seven prizes including best director for Nolan and best actor for Murphy.
Poor Things won five trophies and The Zone of Interest scored three.
