The Department for Work and Pensions is owed £1,046,514.16 from its 10 biggest debtors after they were mistakenly given too much income support, junior minister Helen Goodman said.

Five claimants owe the department more than £100,000, with the highest debt standing at £136,567.94.

The Tories described the figures as "shocking" and called on the Government to tighten controls.

Shadow work and pensions minister Andrew Selous, who uncovered the numbers through a written parliamentary question, said: "It is unforgivable that while taxpayers are tightening their belts, the Government is racking up more debt through poor administration.

"We can't go on like this. Ministers urgently need to get a grip and make sure claimants are paid the correct amount."

Around £800 million is mistakenly paid out in benefits every year, according to official estimates, including £120 million in income support.

Junior minister Helen Goodman said a special taskforce has been set up to tackle debtors who owe more than £10,000.

It has recovered £1.2 million since being brought in last October, she said, and the department has increased overpayment recoveries from £180 million a year in 2005-06 to more than £280 million now.

"We try and stop overpayments occurring in the first place," Ms Goodman said.

"The department's error reduction strategy will help to achieve this. It is based on preventing new error from entering the system, ensuring that customers and staff comply with benefit rules and identifying and correcting existing errors."

Income support is paid to people on low wages who do not have to sign on as unemployed, and is made up of three parts: personal allowances, premiums and payments to cover certain housing costs. The amount paid depends on an individual's circumstances.