The British Government has secretly calculated there are about 500,000 illegal immigrants in the country even though ministers have said they are not aware of the scope of the problem, a newspaper reported.
The research was ordered by Prime Minister Tony Blair more than a year ago "as a matterof urgency" after he hosted a summit on immigration, the Sunday Times newspaper reported, citing a confidential memo.
But in the face of Conservative Party charges of lax border controls, experts conducting the research were told not to disclose the figures, the newspaper said.
According to latest polls, Blair's Labour is on target for its third election victory on May 5, although one gave him a lead of just one point.
A Sunday Times poll suggests the Conservatives' campaigning on emotive issues such as immigration may be bearing fruit.
