* Immigration among voters’ top concerns

* Cameron has said his government has sharply cut numbers

* Report casts serious doubt over accuracy of migration data

By Andrew Osborn

LONDON, July 28 (Reuters) – The success of British Prime
Minister David Cameron’s flagship immigration policy was called
into serious question on Sunday, dealing him a potential blow
ahead of 2015 elections by playing into the hands of a populist
anti-immigration party.

A report by lawmakers from across the political spectrum
concluded that Britain’s migration statistics were grossly
unreliable and “not fit” for purpose, undermining the
credibility of Cameron’s assertions about the issue.

Immigration is a hot button issue in Britain, where Cameron
is trying to stop an exodus of voters to the UK Independence
Party (UKIP) before a parliamentary election in two years’ time,
and polls show the issue is one that worries voters the most.

Concerns have been fuelled by warnings in the right-leaning
press about “hordes” of Romanians and Bulgarians moving to
Britain next year when EU freedom of movement restrictions
lapse, at a time when Britons face rising competition for jobs.

To compound Cameron’s problems on immigration, a government
pilot scheme that involves vans driving around London with
billboards telling illegal immigrants to “go home or face
arrest” has angered his junior coalition partner, the Liberal
Democrats, and prompted allegations of racism.

Questioning immigration was for years regarded as racist in
Britain, but all three main parties have started to talk tough
about the subject in response to rising public anxiety,
campaigns in the country’s popular tabloid press, and the
popularity of the anti-immigration UKIP.

Cameron’s ruling Conservatives, who are trailing the
opposition Labour party in the polls, have promised a
far-reaching immigration crackdown and say they have cut net
migration – the numerical difference between people coming in
and out of the country – by a third.

They have also pledged to cut that figure to tens of
thousands of people a year from over 100,000 now.

DATA ‘TOO UNCERTAIN’

But the report, by the lower house of parliament’s Public
Administration Committee, said that government migration data
was neither systematically nor rigorously collected.

“We are struck by the advice of the Migration Advisory
Committee to the Government that it should aim for net migration
of only 50,000 as the only means of being certain that net
migration is in fact below 100,000,” it said.

Bernard Jenkin, a Conservative lawmaker who oversaw the
report, told local media government statistics were “little
better than a best guess and could be out by tens of thousands.”

Chris Bryant, a Labour lawmaker, said the report showed the
government’s assertions on immigration could not be trusted.

“We should be able to count people in and out of this
country,” he told Sky TV. “If the government is going to boast
about having cut net migration then you would think that the
statistics would be reliable ones. The truth is they’re not.”

Cameron’s Conservatives are trailing Labour in the polls,
but several surveys show Labour’s lead, which until recently had
been fairly steady at ten percentage points, is narrowing.

One opinion poll published earlier this month put the
Conservatives in joint first place with Labour for the first
time in over a year.

UKIP, which campaigns for Britain to leave the European
Union and for a halt to “open door immigration,” made sweeping
gains in May local elections, winning almost one in four votes.

But its poll rating has since fallen from a high of 22
percent. Some polls suggest it has lost one or two percentage
points. Others suggest its fall in support may be more serious.

A spokesman for Britain’s Home Office (interior ministry)
said the government was confident it was on the right track.

“We disagree with the report’s conclusions,” he said.
“Government reforms on immigration are working and the
statistics do show that net migration is at its lowest level for
a decade.”