Neither Shakespeare's plays nor Woody Allen's films prepared Kenneth Branagh for the raging "storm of hormones" he met while filming "Harry Potter and the Chamber of Secrets," opening Nov. 15.

As Gilderoy Lockhart - the golden-haired, narcissistic Defense Against the Dark Arts teacher - the 41-year-old Branagh was the new kid on the block, dropping into a cast of 300 children who'd filmed the last Harry Potter film together the year before.

So there he was in Leavesden Studios outside London, playing teacher in a classroom of fidgety 13-year-olds - only to find notes being passed around under the tables and a definite sexual tension in the air.

"It felt like I had entered while a storm of hormones had burst into the studio," Branagh told The Post.

"Someone fancied someone who fancied someone else, and there were side glances, faces reddening, heads turning" - none of which, he notes, was in the script, which largely concerns itself with Harry's second year at Hogwart's School of Witchcraft, and the horrific beast that's literally petrifying the students.

"The most frustrating thing," Branagh says, laughing, "was not being able to figure out who fancied who!"

Branagh says that while director Chris Columbus didn't film the note-passing, he did catch that "under-the-skin excitement" of children in their first flush of puberty.

"It sounds so clichéd," says this veteran of the Royal Shakespeare Company, "but you do learn from [children]. "They have a directness, an ability to be in the moment of the scene."

Branagh also learned from his elders. During a week's shooting on location in Gloucester, he stayed in a small hotel with fellow castmates Alan Rickman, Maggie Smith, Miriam Margolyes and Richard Harris, who died last week.

"What a pleasure it was to hear relaxed, highly experienced actors telling stories about Brando, Olivier and Julia Roberts!" Branagh says.