British authorities are surprised by this? They think this school is “extremist”?

It isn’t. These teachings are mainstream Islam:

“Men have authority over women because Allah has made the one superior to the other, and because they spend their wealth to maintain them. Good women are obedient. They guard their unseen parts because Allah has guarded them. As for those from whom you fear disobedience, admonish them and send them to beds apart and beat them.” — Qur’an 4:34

Muhammad “struck me on the chest which caused me pain, and then said: Did you think that Allah and His Apostle would deal unjustly with you?” — Aisha (Sahih Muslim 2127)

Muhammad said: “If a husband calls his wife to his bed [i.e. to have sexual relation] and she refuses and causes him to sleep in anger, the angels will curse her till morning” (Bukhari 4.54.460).

He also said: “By him in Whose Hand lies my life, a woman can not carry out the right of her Lord, till she carries out the right of her husband. And if he asks her to surrender herself [to him for sexual intercourse] she should not refuse him even if she is on a camel’s saddle” (Ibn Majah 1854).

“Islamic school accused of warning girls not to use tampons,” by Adam Smith, Metro, May 11, 2018 (thanks to The Religion of Peace):