About 91,000 people from new eastern member states of the EU registered to work in the UK in the five months since the May expansion, figures have shown.
David Blunkett hailed the scheme as a success
The worker registration scheme was created in response to concerns about an influx of migrants.
However, ministers said up to 45% of those registered were in the UK before 1 May, possibly working illegally.
About 2,800 claims for child benefit were received, and fewer than 500 tried to obtain unemployment benefits.
There were 90,950 applications for worker registration from the eight states, Home Secretary David Blunkett said.
The largest group by nationality to register were Polish with 56%, followed by Lithuanians (17%), Slovaks (10%), Latvians and Czechs (both 7%), Hungarians (3%) and Estonians (2%).
EU WORKER REGISTRATION
Slovenian: less than 0.5%
Source: Home Office
Slovenians were given as less than half a per cent.
From May, people entering the UK from the eight eastern European states were allowed to work here if they signed up to the registration scheme.
The idea was to help fill vacancies in areas such as agriculture, catering and construction, but deter people who simply wanted to claim benefits.
"Our commonsense approach to EU enlargement has put us at a clear advantage compared to the rest of Europe," Mr Blunkett told a TUC conference on migrant working on Wednesday.
"Illegal workers have legitimised their status and are contributing to the economy, benefiting from protection in the workplace and allowing us to focus resources on other forms of illegal working."
There was a peak in registration in early summer, with a considerable fall in August and September, the minister said.
There was also "anecdotal evidence" that many had already returned to their home countries, particularly agricultural workers.
The Conservatives were quick to pick up on the figures in attack on government policy.
David Davis, the shadow home secretary, said "Regardless of how the government tries to spin these figures, the fact is our immigration system is still a shambles."