A man who brandished a knife outside one of the country's most prestigious prep schools is reportedly on the counter-terror watchlist.

The man, 49, who is said to have shown an interest in extreme Islamist ideology, was seen carrying a knife near to Godstowe School, in High Wycombe at around 8.10am on Thursday.

He was arrested shortly after pupils and parents gathered near the gates of the school, which counts Lady Gabriella Windsor as a former student.

The suspect, from High Wycombe, tried to run away after police officers challenged him.

Officers threatened him with Tasers and were able to disarm and detain him before armed units were deployed.