European migrants will have to have been earning £150 a week for three months before they can access most UK state benefits, the work and pensions secretary has announced.

Iain Duncan Smith has decided that from March all EU migrants will have to reach this threshold in order to qualify for "worker" status.

David Cameron has been drip-feeding a series of measures to reduce the attractiveness of the UK for EU migrants unlikely to find full-time work here.

People who have been classed as workers under the Department for Work & Pensions rules will then be able to claim child benefit and child tax credit, jobseeker's allowance if they lose their employment, and housing benefit.

But the DWP interpretation of what constitutes a worker is likely to be controversial since it admits the EU definition is unclear.

The earnings threshold will be set at the level at which people start paying national insurance: £149 a week in 2013-14, and £153 a week in 2014-15.

The £150 threshold is equivalent to working 24 hours a week at the national minimum wage.

Anyone with earnings below that threshold will face a fuller assessment of whether their work was "genuine and effective", with the possibility of being denied worker status.

Where a decision is made that an EU migrant should not be considered a worker, then they would be classed either as a jobseeker or economically inactive, which would restrict their access to the welfare system.

The former will have to wait three months before getting income-based jobseeker's allowance (JSA) and, after the introduction of new rules on 1 April, will be ineligible for housing benefit.

Those deemed not economically active would need earnings above income support levels and comprehensive sickness insurance to be eligible to claim child benefit or child tax credit.

The DWP claims that under EU case law, work must be genuine and effective, and not on so small a scale to as to be "marginal and ancillary". The department says there is not clear definition of what ancillary means in this case.

Duncan Smith said: "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."

The government has already announced that after three months, migrants will also have to take a stronger, habitual residence test if they want to claim income-based JSA.

If they pass that test, jobseekers from the rest of the European Economic Area will then only be able to get JSA for six months. After that period, only those who have a job offer or compelling evidence that they have a genuine chance of finding work will be able to continue claiming.