Shamima Begum, the woman who claims that as a schoolgirl she was trafficked to Isis for sex, knew what she was doing and must have been aware of the terrorist group’s “uncompromising brutality”, MI5 said.

Begum began a new appeal yesterday against the stripping of her British citizenship with her legal team arguing she was cynically recruited, groomed and trafficked to Syria before being married off to an older man within days of her arrival in 2015.

MI5’s assessment is that Begum still poses a serious security risk to Britain and that, as an A-star pupil, it was “inconceivable” that she did not know what she was doing.

Giving evidence at the Special Immigration Appeals Commission (Siac), an MI5 official known only as Witness E