I've decided to contact the channel and ask the question.
This is the answer I received:
There are several such moments - e.g. flashes during the school play,
that ends with a kissing scene between the Prime Minister and his
office employee, or earlier, during the Christmas party for the
employees of the character portrayed by Alan Rickman. The last moments
of the film, where the pictures of the people greeting at the airport
multiply are also treated as containing stroboscopic effects.
Adding information about the stroboscopic
effects and/or flashing lights (that could cause seizures in those
suffering from photosensitive epilepsy) before the projection is required by Ofcom (...).
CBS Europa channel broadcasts on the basis of a license issued by Ofcom.
CBS Europa is a Polish channel owner by CBS/AMC. The email was in Polish, the translation is mine.
the government-approved regulatory and competition authority for the
broadcasting, telecommunications and postal industries of the United