Absent parents are withholding tens of millions of pounds from children in Sussex, shocking new figures reveal.

The Child Support Agency (CSA) is pursuing nearly 14,000 parents in the county for refusing to pay a total of £34 million towards their offspring's upkeep.

It comes to an average of £2,500 per family.

By far the biggest child debt blackspot in Sussex, and the eighth biggest in the UK, is Hastings and Rye, where 1,500 non-resident parents owe £4.2 million.

In second place, in Crawley, 1,200 parents owe £3.1 million. More than £2 million is owed by parents in Eastbourne, Bognor and Littlehampton, Wealden, East Worthing and Shoreham and Brighton Kemptown.

The area with the lowest amount of debt is Mid Sussex, where 600 parents owe a total of £1.4 million.

The Conservative Party, which published the figures, blamed the high levels of unpaid debt - amounting to £3.7 billion nationally - on the Government's "failure" to reform the troubled CSA. It said half the cash was unlikely to end up with the children who needed it.

In 2006, the Government invested £120 million in the CSA, adding 1,000 new staff, as part of an Operational Improvement plan. But the Conservatives said the Agency was still "underperforming".

A new Child Maintenance and Enforcement Commission would help improve collection from 2010 but until then thousands of families were "missing out on payments that could help to lift them out of poverty".

Chris Grayling, Shadow Work and Pensions Secretary, said: "The continued failure to get to grips with this problem is undermining the Government's efforts to tackle child poverty.

"It really isn't good enough that so many lone parents are still waiting for financial help, sometimes after waiting for years. Ministers keep telling us they are getting to grips with the problem, but little actually seems to be happening."

Norman Baker, Liberal Democrat MP for Lewes, said: "It is getting better judging by my post bag, but virtually every surgery I do with my constituents someone will raise the issue.

"It's certainly a problem."

James Plaskitt, minister for the Child Support Agency, said improvements had been made and the system was "moving in the right direction".

He said: "Our commitment is to get more money for more children, while reducing child poverty. It is therefore reassuring to see that by the end of last year, the volume of uncleared, new applications had fallen by more than 7,000 since September 2007 and is at its lowest point for more than four years.

"All the other key indicators, such as the amount of money collected and even the number of calls being answered, are also moving in the right direction."