Como dizer "Autuado em flagrante" em inglês

I agree with both, Donay and Adrian. Adrian's expression has a more colloquial ring to it.
Caught in the act is short for "caught in the act of committing an indictable offense." in legalese. Someone could be caught in the act of lying, cheating on their significant other, cheating on the exam, etc.
Usually, which 'act' is specified, sometimes afterward and other times it has been specified before.

The police caught the robbers in the act of ransacking another house.
(here could be implicit that they were arrested, in a newspaper that could also be stated previously, in a headline).

Minha sugestão é a de que se use "caught in the act and arrested".

Ex.: Six high-wire thieves in Delta were caught in the act and arrested. - Canada.com

A forma correta é essa gente, eu estou elaborando um material para um aluno meu policial e fica assim . The bandit was caught red-handed and will be booked in the act for robbery and receiving., (o bandido foi pego em flagrante e será autuado em flagrante por assalto e receptação

Achei no noticiário de hoje no CNN sobre o motim em Londres:

I saw plenty of looting over the next few days but that was the only time I saw someone getting caught in the act.

Talvez:

He's been caught red-handed and arrested.

Não acho necessário traduzir "e será levado imediatamente à delegacia", mas isso depende do que você quer dizer. De qualquer forma, acho que essa última parte ficaria assim: "and (he) will be taken to a police station as soon as possible"

Donay, podemos usar "catch in the act" para o âmbito juridíco? Já que a expressão autuado em flagrante só é usada dentro dele.

Uma dica:

Falso cognato: flagrant