MP Peter Bone insists he is "totally innocent" of allegations of benefit fraud, after his home was raided by police.
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.
Changes to council tax benefits have weakened work incentives for almost a quarter of a million people in England, some of whom stand to lose as much as 97p out of every extra pound they earn, a parliamentary report has found.
The chair of the House of Commons Public Accounts Committee, Margaret Hodge, branded the outcome "fundamentally perverse" saying that the decision to give local authorities powers to design support schemes for themselves has delivered the opposite result to what the Government intended
Council tax benefit was formerly administered nationally, costing taxpayers £4.3 billion in 2011/12 as five million people claimed support.
From April 2013, responsibility was transferred to 326 local authorities in England, with the Government providing funding of £3.7 billion - a cut of £414 million, or 10% of the predicted total budget if the scheme had remained unchanged.
EU citizens wanting to claim certain benefits - including child benefit, child tax credit and housing benefit - will have to have been earning £149 a week for three months to qualify. It is the level at which someone starts paying National Insurance contributions.
If a claimant has been earning below this level then they will be assessed by the Department for Work and Pensions to determine whether their work is 'genuine and effective' - the test set by the EU for entitlement to benefits.
This new earnings threshold was announced two weeks ago but is coming into force today.
The Department for Work and Pensions has defended the new Personal Independence Payment, after a report suggested claimants were having to wait longer for their claims to be processed.
Margaret Hodge said the claims would cost almost three and half times more to process than the previous Disability Living Allowance system, and claimed the delays would cause "real distress" for vulnerable people.
However, the DWP defended the scheme claiming the previous system was "broken".
PIP is a completely new benefit with a face-to-face assessment, something missing under DLA, and there will always be initial costs so this is not comparing like with like.
The figures show good value for money for taxpayers in the short and long term, with expected savings of £3 billion annually by 2018/19.
Delays in processing claims under the new Personal Independence Payment have reduced the amount the Government expected to save by £140 million, the National Audit Office said.
The backlog in cases have cut expected savings over the course of this Parliament, with the DWP now forecast to save £640 million a year by 2015, rather than its orginial prediction of £780 million.
Each new PIP claim - worth between £21 and £134 a week to disabled claimants - costs an average £182 to administer, compared to £49 under DLA, the report said.
However, the DWP said it still expects to achieve annual savings of £3 billion by 2018/19, with 3.6 million claims assessed by 2018.
Delays in processing the Government's new Personal Independence Payment (PIP) will cause "real distress for vulnerable claimants", the Public Accounts Committee chair has said.
Margaret Hodge said claimants were left facing "uncertainty and potential financial difficulties", after the National Audit service found claimants were having to wait longer for claims to be processed than under the previous system.
"I was shocked to learn that, not only will Personal Independence Payment claims cost almost three and half times more to administer than Disability Living Allowance, they also take double the amount of time to process," the Labour MP said.
"The current backlog and delays in processing claims are simply unacceptable and will no doubt cause real distress for vulnerable claimants."
Benefit claimants face "long and uncertain delays" as a consequence of the slow processing of claims under the Government's new Personal Independence Payment, the National Audit Office said.
The head of the NAO Amyas Morse claimed the Department of Work and Pensions did not allow enough time to see if the assessment process could handle a large number of claims.
Mr Morse added:
The Department did not allow enough time to test whether the assessment process could handle large numbers of claims.
As a result of this poor early operational performance, claimants face long and uncertain delays and the Department has had to delay the wider roll-out of the programme.
Because it may take some time to resolve the delays, the Department has increased the risk that the programme will not deliver value for money in the longer term.
Disabled people are facing "distress and financial difficulties" as a result of the slow processing of claims under a new Government benefit scheme, a spending watchdog has found.
The National Audit Office found that claimants for the new Personal Independence Payment, which will replace Disability Living Allowance, were waiting an average 107 days for a decision on their cases, rather than the predicted processing times of 74 days.
Terminally ill patients were found to be waiting for 28 days instead of 10 days.
A backlog of 92,000 cases had built up with private contractors Atos and Capita within six months of the introduction of PIPs in some areas of the north of England.
Conservative MP Peter Bone said allegations in relation to an inquiry into benefit fraud against his family are "without foundation."
The Times reported that the Wellingborough MP had been questioned as part of a inquiry into benefit claims to pay for the residential care of hie mother-in-law, Dorothy Sweeney. Anyone with assets over £23,250 is expected to pay their own care home fees.
The paper alleges Northampton County Council was not given accurate information about Mrs Sweeney's assets before paying benefits of around £100,000. Writing on Twitter, Mr Bone said:
The Times allegation: We have done nothing wrong. The claims made are without foundation. A full statement will be issued in due course.
Denying "worker" status to EU migrants who fail to prove they have earned £150 per week for at least three months will curb benefits tourism, Iain Duncan Smith has said.
The work and pensions secretary explained:
– Iain Duncan Smith
As part of the Government's long-term economic plan we have taken action to make sure our economy delivers for people who want to work hard, play by the rules and contribute to this country.
These reforms will ensure we have a fair system - one which provides support for genuine workers and jobseekers, but does not allow people to come to our country and take advantage of our benefits system.
The British public are rightly concerned that migrants should contribute to this country, and not be drawn here by the attractiveness of our benefits system.