Staff at the beleaguered Child Support Agency were paid £25 million in bonuses over the past five years, according to latest figures.
Some £4 million was paid out last year, when the Government announced it was abolishing the agency because of poor performance.
The agency, responsible for collecting child maintenance payments, has failed to collect £3.5 billion, millions of pounds of which has already been written off.
Shadow work and pensions secretary Philip Hammond said families who had lost out because of the CSA would ask whether the money could have been put to better use.
"The magnitude of this figure will come as a shock to the 1.4 million families stuck in the failing CSA system," he said.
"Families trapped in the CSA will rightly ask whether this money could have been put to better use in a system where £3.5 billion debt remains uncollected and 250,000 cases languish on a backlog," he said.
Last year, the Government announced the CSA would be scrapped and replaced with a new body with stronger sanctioning powers.
But Opposition MPs criticised the move to the Child Maintenance and Enforcement Commission (C-Mec), which will be able to dock wages, impose curfews and "name and shame" defaulters.
They said it would not come in to force until 2010 and today the Tories urged ministers to fast track the plans.
Mr Hammond said: "John Hutton should be doing a lot more for these families by fast-tracking some of the proposals for the replacement Child Maintenance system to benefit existing CSA families right now."
