Single parents in parts of the UK are owed millions of pounds in unpaid child maintenance, a new study shows.
More than £6 million is owed in areas of West Yorkshire, Milton Keynes, Grimsby, Telford and Nottingham, said campaign group Gingerbread.
The lowest arrears were found to be in parts of Sheffield, the Outer Hebrides and London.
The charity for single parent families claimed the Child Support Agency (CSA) was doing less to collect debts as it winds down, with its work being transferred to the new Child Maintenance Service.
Gingerbread chief executive Fiona Weir said: "Bringing up children costs money and both parents have a responsibility to contribute financially.
"The failure of the CSA to collect these millions of pounds of child maintenance means that children are going without and single parents have been left poorer. Child poverty in single-parent families is set to double in the next four years, so it's even more essential that this money is collected.
"The CSA and its successor the CMS should be doing all they can to ensure that families get the financial support they are owed. They have many powers at their disposal but in reality both are slow to act when parents don't pay and single parents are left shouldering the costs of raising a child alone."
A Department for Work and Pensions spokesman said: "We actively pursue those parents who are not meeting their financial responsibilities and in almost 90% of cases, parents are paying the money owed.
"We have measures in place to ensure that no client will get lost when debt is transferred from the old system."