Britain's taxpayers are forking out more than £21million a year in child benefit for youngsters living in Poland, official figures reveal.
A loophole in EU regulations means migrants from other EU countries who are seeking work in the UK can claim state handouts for children they have left behind in their home countries.
The total benefits bill for the Treasury is likely to be closer to £50million a year when other Eastern European countries are included.
In addition, ministers refuse to reveal how much more is being paid out in tax credits. Last night, the revelations prompted demands for a shake-up of the rules, with critics complaining of a "Government-sanctioned scam" at a time when millions of British children remain in poverty.
Britain's child benefit payments of £941 per year for a first child or £629 per year for younger siblings are far higher than the equivalent paymentsin Eastern European states that are new EU members.
The Polish benefits system, for example, pays a maximum of around £160 per year in child benefit.
Investigations have found that many workers moving to Britain are fraudulently claiming family benefits in both countries, exploiting lax checks and poor information sharing between member states.
Figures released by the Treasury in answer to Parliamentary written questions from the Conservatives show that at the end of September 26,000 Polish children from 16,286 families were being paid child benefits by UK taxpayers.
That means 16,286 first-born children were receiving the full £18.10 per week with the remaining 10,000 getting the lower payment of £12.10 per week.
The figures show that the number of claimants is soaring.
In June last year, the Treasury said 14,000 families from eight Eastern European states were claiming the benefits - around 10,000 were estimated to be Polish.
Open borders: More than 700,000 workers from Eastern Europe have arrived in Britain in the four years since their countries joined the EU
Three months later the figure for Poland alone had risen to 16,286.
At this rate of increase the benefits bill could more than double in a year, with thousands more Eastern European families joining in the benefits bonanza.
Although all the payments are legal under EU law, critics claim they provide an added incentive for immigrants to come to the UK.
Britain was one of the only EU states to give workers from eight Eastern European states full access to its jobs market when they joined the EU in 2004.
They were: the Czech Republic, Slovakia, Estonia, Latvia, Lithuania, Slovenia, Hungary and Poland.
Romania and Bulgaria joined the EU a year ago.
Ministers predicted that around 13,000 workers would arrive in Britain each year. In reality more than 700,000 have arrived, more than half from Poland.
Polish newspapers regularly run features explaining exactly how to claim benefits in the UK.
Once EU nationals have been working and paying tax in Britain for 12 months, they are entitled to the same level of state support as any British citizen, including child benefit for their children living in another EU country.
A spokesman for HM Revenue and Customs said claimants had to provide evidence to support claims for children abroad, such as a birth certificate.
It is thought that even larger sums are being paid out to Eastern European workers in tax credits - financial support provided through the tax system for those with children or on lower incomes. Ministers say, however, that total figures are "not available".
Conservative MP Andrew Selous, who uncovered the latest figures, said: "This shows there is a need for a serious reassessment of this aspect of the welfare state.
"The Government still refuses to answer how much child tax credit is paid to migrant workers whose children live abroad. They have shown no leadership or political will in trying to sort out this issue."
Shadow Home Secretary David Davis said: "When will Gordon Brown get a grip?
"Some 3.8million British children are living in poverty and yet £21million of taxpayers' money is going to Poland because our benefits system is such a shambles.
"We need to know how much this Government-sanctioned scam is really costing the taxpayer."
Sir Andrew Green, chairman of the MigrationWatch think tank, said: "It makes absolutely no sense to pay benefits at British rates for children in a country where the cost of living is a fraction of ours.
"It is time these EU arrangements were renegotiated."