LONDON — British intelligence and police units are using children in undercover operations in a drive to expose terrorists, criminal gangs and drug dealers amid a nationwide rise in violent crime.

A House of Lords committee revealed the practice last week after reviewing the government’s new draft of legislation that seeks to extend the period for which youths under the age of 18 are authorized to work as a “covert human intelligence source.”

The Home Office has asked to extend the period in which a child is authorized to serve as an undercover informant to four months, from one month. The proposed legislation comes as violent crime in England and Wales has jumped, with murders up by 12 percent over the same period last year, according to figures published by the Office of National Statistics.

“We are concerned that enabling a young person to participate in covert activity for an extended period of time may expose them to increased risks to their mental and physical welfare,” The House of Lords secondary legislation scrutiny committee said in a report released on July 12.