Britain remains the most lucrative destination in the European Union for Romanians and Bulgarians with a "generous" welfare system providing a major incentive for migrants despite new curbs being introduced, it has been claimed.
David Cameron has rushed through a plan to introduce a three-month wait before EU migrants can claim out-of-work benefits so it coincides with the end of temporary controls tomorrow that had blocked citizens from the two countries moving to the UK.
But the reforms do not affect welfare payments for claimants with jobs, meaning migrants will still have more in-salary and in-work benefits than in any other major European country, according to Migration Watch UK.
Business leaders, however, have said lifting the restrictions will help "cement our economic recovery" as well as fill the gap in the number of skilled workers companies need.
Lifting the transitional controls to give citizens of the two countries unrestricted access to the UK labour market from New Year's Day has become a flashpoint in the increasingly bitter debate over immigration in Britain.
Research by Migration Watch UK suggests some of the two million Romanians and Bulgarians already living in Spain and Italy could choose to move to northern European countries where there are "considerably greater" financial rewards.
A worker with a spouse and two children on half the average wage in Romania or Bulgaria would be three times better off in Spain or Italy but six times better off in the UK, according to its report.
The think-tank found that Germany remains the "most attractive destination" with its low unemployment rate and large number of vacancies, but reiterated its previous analysis predicting that 250,000 Romanians and Bulgarians will move to the UK over the next five years.
Migration Watch UK chairman Sir Andrew Green said: "This study shows how Britain's generous benefits system acts as a pull factor for migrants from across Europe.
"There must now be a renegotiation of the benefit system in the EU which was designed before 100 million people in much poorer countries joined the EU. British taxpayers must no longer subsidise immigration from poorer parts of the EU."
The London Chamber of Commerce and Industry said that 55% of its members believe immigration has had a positive impact on the capital's economy and more than half employ migrant workers.
Chief executive Colin Stanbridge said: "Political rhetoric on migrant workers has stepped up in recent days as the deadline for removal of restrictions approaches. However, the debate often fails to take into account the positive benefits that migration brings to the London economy.
"Migrant workers are often highly skilled, bringing with them knowledge and experience that London businesses badly need - now - in order to continue to grow.
"Of course the Government needs to equip our young people with the skills that businesses require, but that will take years.
"The Government has allowed the debate about Bulgarian and Romanian migration to become highly politicised when, in fact, giving London businesses access to a larger labour pool will help cement our economic recovery."
The UK imposed the seven-year restrictions on Romania and Bulgaria after they joined the EU in 2007 - only allowing citizens a visa if they were self-employed, had a job offer, or were given a specialist role.
Backbench Tory MP Nigel Mills's amendment to the Immigration Bill would extend transitional arrangements on the two countries joining the European Union's freedom of movement rules by a further four years to 2018.
Work and Pensions Secretary Iain Duncan Smith insists the reforms that have been pushed through will "not allow people to come to our country and take advantage".
After six months on Jobseekers' Allowance of up to £71, only those who can provide compelling evidence that they have a genuine chance of finding work will be allowed to continue claiming the benefit.
Claimants, including Britons returning from overseas, will also face a tougher ''habitual residence'' test to prove where they live, including face-to-face interviews, before they receive any JSA payments.
Mr Duncan Smith said: "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.
"That is why, as part of the Government's long-term economic plan, we have taken action. New rules are now in place to 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.
"I know that other countries across Europe share our concerns, so we'll continue to work with them to ensure we can protect the integrity of our benefits system."