Immigrants to the UK are being tested on their English skills before being able to claim income-related benefits under a new scheme.
People are being asked what efforts they have made to find work before coming to Britain.
Work and Pensions Secretary Iain Duncan Smith said people should not be able to "take advantage" of British benefits.
Labour supports English tests but says ministers are ignoring the exploitation of low-skilled migrant workers.
UKIP spokesman dismissed the move as "gesture politics" and said "a far more effective filter, if we had control of our borders, would be to have migrants learn English before they come to the UK," something, he added, that would be illegal under EU law.
Job centres in England, Scotland and Wales began using the "more robust" language tests on Monday and they are being rolled out to all centres.
The Department for Work and Pensions (DWP) said the test would ensure "only migrants who have a legal right to be in Britain and plan to contribute to this country can make a claim for benefits".
"For the first time, migrants will be quizzed about what efforts they have made to find work before coming to the UK and whether their English language skills will be a barrier to them finding employment," the DWP said in a statement.
DWP sources said the tests apply to everyone whether they are a migrant or not.
The language element, in the context of migrants, "will be taken along with all the applicant's other answers and evidence to assess their links to the country and their chances of getting a job," the source added.
Income-related benefits include council tax benefit, housing benefit, income-based jobseeker's allowance and pension credit.
Mr Duncan Smith said British people were "rightly concerned" that migrants should contribute to the economy and should not be "drawn here by the attractiveness of our benefits system".
"It is vitally important that we have strict rules in place to protect the integrity of our benefits system," he said.
He said the new test would help create a fair system which provided for "genuine" workers and jobseekers but "does not allow people to come to our country and take advantage".
To claim the benefits, migrants will have to pass a "habitual residence test" including more than 100 extra questions compared to now.
'Bad for everyone'
This will be overseen by an "intelligent IT system" which will ensure questions are "tailored to each individual claimant".
Migrants will be allowed to claim benefits if they can prove they are legally allowed to be in Britain and are "habitually resident" the country.
As part of this they might be questioned about what measures they have taken to "establish" themselves in Britain and what ties they still have abroad.
"They will also have to provide more evidence that they are doing everything they can to find a job," the DWP said.
Labour's shadow welfare minister Chris Bryant said: "For generations, people have come to this country and worked hard to contribute to Britain, but the principle of contribution is an important one, and the controls on immigration must be fair to those who live here.
"That is why Labour called for stronger restrictions on benefits for new arrivals from the EU, including proposals eight months ago to strengthen the habitual residence test to make it clear that people should not be able to claim benefits when they first arrive."
He accused ministers of "still doing nothing to tackle the serious problem of low-skilled migrant workers being exploited, undercutting local workers and responsible businesses too".