Prime Minister Gordon Brown has joined the families of murder victims to launch an online campaign aimed at tackling knife crime. Skip Mr Brown said relatives of victims were able to give "the most powerful warning there is" about the effects of using a weapon. Primary schools in knife crime hotspots will also be given information to help teachers tell children about the dangers. The Government is working with the charity Families Utd, which represents victims' relatives, to launch the Count Me In: Together We Can Stop Knife Crime week. The mother of murdered 18-year-old Harry Potter actor Rob Knox backed the campaign. Sally Knox said: "I truly believe that we need to get into schools and educate young people about street violence and respect. Together with the other families who have suffered similar tragedies and the Government we can make a difference to the future of young people on our streets."