The Child Support Agency will not replace its troubled computer system, even though it will not work fully for two years, the government has said.
The CSA system was meant to be fully functional by 2003
Work and Pensions Secretary John Hutton told the Commons work and pensions committee changing it would cost £456m.
It was also outside the remit of a CSA review launched last week, he added.
The computer system was originally supposed to be fully functional by 2003. Labour MP Anne Begg said the government should "just pull the plug".
Fit for purpose?
Mr Hutton last week announced the appointment of former Liverpool City Council chief executive Sir David Henshaw to carry out a "radical redesign" of the CSA.
Conservative MP Justine Greening asked whether this meant the government was prepared to pull out of the contract with supplier EDS if the computer system was found to be not "fit for purpose".
Mr Hutton said that was "not what I expect him (Sir David) to recommend".
The committee has previously criticised EDS after the computer system failed, leaving thousands of single parents struggling without maintenance payments.
CSA chief executive Stephen Geraghty told the committee the system would not be operating to the agreed delivery specifications until the end of 2007.
One million cases
It would take until the end of this year to clear the 200 "defects" which had been blamed for 70,000 cases becoming "stuck" in the system.
However, with one million cases on the computer and the contract with EDS due to run to 2010, Mr Geraghty said it was not realistic to consider pulling out.
If the company failed to deliver the promised improvements by the end of 2007, the government would have the choice of ending the contract early or withholding £17m in payments.
Ms Greening said EDS had the government "by the short and curlies".
Last week, Mr Hutton said the CSA's performance was "unacceptable" and a thorough review of the UK's child support system would be completed by the summer.
In the short term, private debt collectors will be used to help recover arrears of £3bn and the agency given more powers to chase absent parents.
The Conservatives said the government had shown a "lamentable failure" to address the CSA's problems.
Liberal Democrats have called for the agency to be abolished.