Migrants from nations joining the EU in May will have to work or leave the UK, Tony Blair has insisted.
Migrants will be able to work but not claim benefits, says Blunkett
He spoke as Home Secretary David Blunkett announced plans to cope with migrants after EU enlargement in May.
People from the new EU states would not need work permits but would need to be on a work register, said Mr Blunkett.
Migrants without work will be banned from most benefits for at least two years but those working could take some welfare payments immediately.
Earlier, Mr Blair said residents of the eight ex-East European communist countries would only be able to stay if they had jobs.
"If they can't support themselves, they will be put out of the country," he told a BBC radio phone-in.
Britain and the Irish Republic had been the only two EU countries planning to give the unrestricted right to work to people from new EU member states.
That prompted fears there would be an influx of thousands of people.
With most other EU nations imposing restrictions, the home secretary said "it makes sense that our approach will not leave us exposed".
"People who come here from accession countries but do not work will not be able to claim benefits."
That restriction will last until at least 2006. But migrants who work continuously for more than a year will be able to claim benefits like income support or jobseeker's allowance earlier if they lose their jobs.
Those who are working, paying tax and national insurance, will also immediately be able to claim: emergency NHS treatment, council tax benefit, housing benefit, homelessness assistance, child benefit, working tax credit, child tax credit and state pension credit.
Mr Blunkett said there were labour shortages to be filled and he wanted people to be able to work legally.
"Whether they are plumbers or paediatricians, they are welcome if they come here openly to work and contribute."
Insisting on work permits risked pushing migrants onto the black market, where they would pay neither tax nor national insurance, he argued.
Blair talked tough during radio phone-in
The work registration scheme would enable the government to monitor the type and location of jobs taken by new migrants, he said.
"If the registration scheme shows an imbalance in the labour market we will re-impose restrictions."
The measures were agreed at a hastily arranged meeting in Downing Street chaired by Mr Blair last week.
Ministers deny adopting panic measures but shadow home secretary David Davis said there was "chaos and confusion" because decisions had been taken too late.
He predicted there would be large numbers of migrants, which would put "huge pressure" on public services.
Liberal Democrat home affairs spokesman Mark Oaten said the policy should be based on "fact not tabloid fiction".
Rather than introduce measures on the back of predictions of a migrant influx, Mr Oaten said it would be better to review whether controls were needed six months after enlargement.
All existing EU states can impose transitional restrictions for up to seven years on the right of residents of eight of the 10 new EU member states to work and claim benefits.
The restrictions only cover the former communist states joining the EU.
Ahead of Monday's statement, Mr Blunkett said UK border controls may be extended to Belgium in the drive against asylum system abuses.
In a deal with France, British officials are already allowed to check the documents of passengers boarding London-bound Eurostar trains in Paris.