Guidelines being issued say schools must intervene to prevent students, even children of primary age, joining gangs.

According to The Guardian newspaper, this includes gathering proof from computers and evidence such as photographs.

The newspaper also says there is a growing fear that sexual abuse of young girls is becoming a part of gang culture in initiation rituals or revenge attacks.

There is an additional concern that members are targeting younger children.

A spokesman for the Department for Children, Schools and Families said: "It does appear that the issues are growing in some of our inner cities, particularly with more fluid and localised patterns of gang activity and with gang members aiming to draw in younger children."

The guidelines give advice to teachers on how to identify children who may have joined a gang and the action to take if they do.

This includes wearing certain colours, items of jewellery or clothing, sometimes weapon-proof clothes, and looking for graffiti tags in books and on walls, The Guardian reports. There is also emergency advice on what to do if gang violence breaks out.

Children and Young People's minister Beverley Hughes, who will launch the guidelines in Birmingham, said: "The safety of teachers is crucially important and the guidance is clear that heads and teachers should never put themselves at risk in any way.

"But schools can be an important 'first line of response' - helping us to identify those at risk and provide them with the specialist support they need to resist gang culture."