Up to 120,000 of the country's most dysfunctional families are to be identified, visited and advised how to turn their lives around, David Cameron will announce today.

A squad of "troubleshooters" will take charge of efforts to combat the criminality and anti-social behaviour committed by a hard core of problem families.

They will dispatch social workers to visit the worst troublemakers, giving them practical advice on how to run a home and raise a family.

The Prime Minister will say troubled families cost the taxpayer £9bn a year, or £75,000 per household, which is mainly the cost of taking children into care and dealing with the impact of crime, gangs and violence.

Families will be given "clear, hard-headed" advice on their mistakes – and not visits from a "string of well-meaning, disconnected officials who end up treating the symptoms and not the causes". They will be offered help with issues such as finding work, dealing with mental health problems and tackling truancy.

Speaking to charities and voluntary organisations in the West Midlands, Mr Cameron will say: "When the front door opens and the worker goes in, they will see the family as a whole and get a plan of action together, agreed with the family. This will often be basic, practical things that are the building blocks of an orderly home and a responsible life."

The drive will be led by the head of the Government's new Troubled Families Team, Louise Casey, who ran Tony Blair's Respect Task Force. She will oversee the creation of the network of "troubleshooters", appointed by local councils, who will be responsible for pinpointing and contacting the most problematic families in their area.

Funding is being set aside for the programme on the basis that money spent now could soon save the state far more money dealing with the effects of the families' behaviour.

Mr Cameron will say: "I am an optimist about human nature. I don't believe in writing people off.

"I don't think people are pre-programmed to fail because of where they come from and I hate the idea that we should just expect to pay ever larger amounts in welfare to an ever larger chunk of society and never expect the recipients to change their lives."