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.
Some 11 per cent of benefit payments have been suspended since a tougher regime was introduced - check what has changed and how to claim.
- New immigrants will not eligible to out of work benefits for the first three months. If after three months an EU national needs benefits they will only be able to claim for a maximum of six months.
- There will be a new minimum earnings threshold to prevent access to benefits such as income support. Newly arrived EU jobseekers will not be able to claim housing benefit.
- Beggars or those sleeping rough will be removed and barred from re-entry for 12 months.
- There will also be a clamp down on those who employ people below the minimum wage. With a fine of up to £20,000 for every underpaid employee – more than four times the current fine, in an attempt to help native workers.
Shadow home secretary Yvette Cooper says the government are 'flailing' over their immigration policy:
The Prime Minister is playing catch up. Why has it taken him eight months to copy Labour's proposal to make the Habitual Residence Test stronger and clearer?
After Labour proposed this change in March, the Government said it was all fine and nothing needed to change. Yet now, rather than following a coherent plan, they are flailing around.
No wonder public confidence in the Government's handling of this issue has collapsed.
This change was only one of Labour's proposals. The Government should also be beefing up enforcement of dodgy gangmasters and targeting sectors that are reliant on migrant labour to ensure they are working to train employees.
Deputy Prime Minister Nick Clegg insisted his Liberal Democrats were fully signed up to the rule changes - although senior sources stressed that the post-2015 ideas had not been agreed.
These are sensible and reasonable reforms to ensure that the right to work does not automatically mean the right to claim.
Other countries in the EU already have similar policies and are considering the case for going further - unfettered access to benefits across the member states simply does not exist.
Anyone who believes we are better off as an outward facing nation should support these changes. If we don't get to grips with these issues, pro-Europeans surrender the debate to the UKIPs of this world.
David Cameron has pledged to stop new arrivals from the EU getting out-of-work benefits for three months ahead of an expected increase in Romanian and Bulgarian immigrants.
Writing in the Financial Times (£) the Prime Minister said: We are changing the rules so that no one can come to this country and expect to get out of work benefits immediately; we will not pay them for the first three months.
"If after three months an EU national needs benefits - we will no longer pay these indefinitely. They will only be able to claim for a maximum of six months unless they can prove they have a genuine prospect of employment.
"We are also toughening up the test which migrants who want to claim benefits must undergo.
"This will include a new minimum earnings threshold. If they don't pass the test we'll cut off access to benefits such as income support. Newly arrived EU jobseekers will not be able to claim housing benefit."
Downing Street aides said currently some immigrants could access Job Seeker's Allowance (JSA) within a month of arrival in the UK.
David Cameron's official spokesman sidestepped repeated questions from reporters whether the Prime Minister was "confident" that Universal Credit would be delivered on time and on budget.
He said: "The department is working to the 2017 timetable. That is the timetable that the department continues to work to."
Pressed on whether it was right for ministers, rather than senior officials, to take responsibility for failings in implementing major policies, the No 10 spokesman said the Prime Minister had previously insisted that "everyone has to take their responsibility."
The chairperson of the Public Accounts Committee (PAC) said she had not been approached by the Work and Pensions Secretary over singling out the departments' chief civil servant in the report revealing the Universal Credit scheme "wasted £140 million."
The Times reported that Mr Duncan Smith and members of his parliamentary team approached Tory members of the PAC to ensure that the department's chief civil servant Robert Devereux was singled out for criticism.
Sidestepping the question over wider Tory lobbying, she told the BBC:
Iain Duncan Smith didn't approach me. Beyond that I can't comment.
She went on to criticise the "fortress culture" at the Department of Work and Pensions, which meant "only good news was reported and problems were denied".
Commons leader Andrew Lansley said there was "no truth" in allegations that Cabinet minister Iain Duncan Smith tried to blame "shocking" failures in his welfare reform programme on his most senior departmental official.
Mr Lansley said he had spoken to Mr Duncan Smith about allegations that he and members of his parliamentary team approached members of the Public Accounts Committee to ensure that his department's chief civil servant was blamed for the "alarmingly weak" handling of Universal Credit reform.
I have talked to Mr Duncan Smith and I can tell the House that there is no need for a statement.
I can tell you and the House now there is no truth in the allegations made about talking to members of the Public Accounts Committee because I talked to Mr Duncan Smith so I can tell the House.
TaxPayers' Alliance political director Jonathan Isaby says the principle of simplifying the benefits system is right but the implementation is "deeply flawed".
He added: "A horrendous amount of taxpayers' money has already been wasted and those responsible for that must be held to account.
"Such a fundamental reform of the welfare system was always going to be a challenge, but the approach of many officials in the Department for Work and Pensions has been little short of shambolic."
Following criticism of the implementation of Universal Credit, a Department of Work and Pensions spokeswoman has said the scheme will "ultimately bring a £38bn economic benefit to society."
She added: "This report doesn't take into account our new leadership team, or our progress on delivery. We have already taken comprehensive action including strengthening governance, supplier management and financial controls...
"We don't recognise the write-off figure quoted by the committee and expect this to be substantially less. The head of Universal Credit, Howard Shiplee, has been clear that there is real potential to use much of the existing IT. We will announce our plans for the next phase of UC delivery shortly."