Work and Pensions Secretary Iain Duncan Smith has denied claims that his welfare reform programme is a "debacle".
Cameron has outlined plans to stop immigrants from inside Europe claiming various benefits in a move criticised and rubbished by Brussels.
Minister dismisses claims he attempted to pin the blame for "shocking" failures in his flagship welfare reform on his senior official.
The Department for Work and Pensions has confirmed that £40.1 million had been written off on software and computing costs during the introduction of the new Universal Credit system.
Annual accounts will show £40.1m write-off for Universal Credit IT which includes the £34m we previously announced
Re discussion of £90m IT today - we will be using this while we continue to roll out UC over the next five years. Not a write-off.
The Work and Pensions Secretary Iain Duncan Smith has denied claims that his welfare reform programme is a "debacle".
Speaking in front of MPs today, Mr Duncan Smith admitted the introduction of the new system was running late, but revealed the IT problems that initially disrupted the programme were now fixed.
Work and Pensions Secretary Iain Duncan Smith has insisted his flagship welfare reforms remain on track, despite further delays to the programme.
Mr Duncan Smith disclosed last week that his 2017 target for the full introduction of Universal Credit is set to be missed - with around 700,000 claimants facing a longer wait.
Speaking ahead of his appearance before the Commons Work and Pensions Committee, he said the delay was to allow the most vulnerable claimants more time to adjust to the change.
"We could easily have tried to rush those people in but we have decided not to. I think it is only fair to give them longer," he told BBC Radio 4's Today programme.
"I do accept, of course, that this plan is different from the original plan."
Giving evidence alongside Iain Duncan Smith at the work and pensions select committee will be Howard Shiplee, the former London Olympics executive drafted in earlier this year to "reset" the Universal Credit programme amid growing concerns over delays and IT issues.
The Secretary of State may also be questioned about reports - which he denies - that he sought to have MPs pin blame for the failures on the DWP's chief civil servant Robert Devereux.
In his reply to the Autumn Statement, shadow chancellor Ed Balls taunted Mr Duncan Smith, commonly known as "IDS", over the reforms, suggesting it stood instead for "In Deep Shambles".
In written evidence to the committee, the DWP said it was "confident that it has taken, and continues to take, the right remedial steps to address past issues in the Universal Credit programme."
Shadow work and pensions secretary Rachel Reeves said the extent of the delay to the Government's introduction of Universal Credit was set out in data released by the Office for Budget Responsibility (OBR) alongside the Chancellor's Autumn Statement.
David Cameron and Iain Duncan Smith repeatedly promised to deliver their flagship policy 'on time and within budget'. That claim, and the credibility they staked on it, now lie in tatters.
– Shadow work and pensions secretary Rachel Reeves
For months on end the Government have tried to avoid answering questions about Universal Credit but these OBR figures tell the truth of how (they) have broken their promises on a spectacular scale.
They have been forced to admit that they have completely missed their targets and Universal Credit will not now be rolled out before the election. David Cameron and Iain Duncan Smith are presiding over a complete mess and it is taxpayers who are picking up the bill with at least one hundred million pounds of their money written off.
Iain Duncan Smith is to be grilled by MPs over the scale of delays to the Government's flagship welfare reform - Universal Credit.
The Work and Pensions Secretary - who will appear before the Commons committee today - has admitted the 2017 target for the full introduction of Universal Credit is set to be missed - with around 700,000 claimants facing a longer wait.
But Labour said official figures showed that only a tiny fraction of the numbers due to be using the new system by the time of the next general election would be transferred on time.
Only a "handful" of the promised 1.7 million would be switched by 2014/15 and only 400,000 by the following year - less than 10% of the original target, the Opposition said.
Responding to the Government’s admission that Universal Credit behind schedule, Shadow Work and Pensions Secretary Rachel Reeves MP labelled the Coalition as "out-of-touch".
– Shadow Work and Pensions Secretary Rachel Reeves MP
Iain Duncan Smith has today admitted what everyone has known for months – that Universal Credit is massively behind schedule. But just a couple of weeks ago he was telling Parliament the Government would 'roll out Universal Credit on the plan and programme already set out'.
It’s clear that David Cameron and Iain Duncan Smith have completely failed to get to grips with their flagship welfare reform and millions of pounds of taxpayers’ money have been written off as a result. Families facing a cost-of-living crisis deserve better than this.
Universal Credit, the new single payment for people who are looking for work or on a low income, will be rolled out throughout 2013 and will replace benefits such as:
Income-based Jobseeker’s Allowance, the unemployment benefit paid by the government to people who are unemployed and seeking work.
Income-related Employment and Support Allowance (ESA) - for the ill or disabled, ESA offers financial support if you’re unable to work or personalised help so that you can work if you’re able to.
Income Support - for people with no income or a low income who are working less than 16 hours a week and haven’t signed on as unemployed.
Child Tax Credit - can be claimed for each child you’re responsible for if they’re under 16 or under 20 and in approved education or training.
Working Tax Credits - you could qualify if you’re aged 16 or over, work a certain number of hours a week, you get paid for the work you do (or expect to) but your income is below a certain level.
Housing Benefit - to help you pay your rent if you’re on a low income.
Universal Credit is now live in seven areas across the UK and will be growing to ten by spring 2014. By the end of next year, the scheme will expand to cover more of the north west.
But the Government has admitted that about 700,000 claimants of a disability benefit will not be transferred to the new Universal Credit before 2017.
The Universal Credit reforms are intended to help people back into work but the Department for Work and Pensions said its priority throughout had been the "safe and smooth" delivery of the new policy.