Definition: In this task, you need to generate an appropriate title for the given summary of some paragraph. The generated title must be short and should include the main topic of the given text. Your summary should be less than 20 words long.
Input: A former undercover police officer has admitted for the first time that the Metropolitan Police set out half a century ago to infiltrate left-wing political groups, even if they posed no threat to the public.

Undercover officer targeted 'anti-establishment' left