LONDON (Reuters) - An advertising campaign designed to get illegal immigrants to leave Britain opened up a rift in the government on Monday when Prime Minister David Cameron's spokesman said it was working but his coalition partner said the idea was "offensive".
The trial campaign saw two vans drive around six London boroughs in the last week displaying billboards telling illegal immigrants to "Go Home or Face Arrest", part of a wider government crackdown aimed at reducing net migration - the numerical difference between people coming in and out of the country.
Urging people to contact the authorities "for free advice, and help with travel documents", the posters carried a big picture of a pair of handcuffs and reported how many illegal immigrants had been arrested in the last week.
Voluntary immigrant returns were the "most cost-effective" way of reducing illegal migration, officials said.
Immigration is a hot button issue in Britain, where Cameron is trying to stop an exodus of voters from his ruling Conservatives to a populist anti-immigration party before a parliamentary election in two years' time.
Conservative strategists believe the campaign will be popular with many voters, but the topic is an uncomfortable one for Cameron's junior coalition partner, the left-leaning Lib Dems.
Keen to distance themselves from the Conservatives in voters' minds before the next election, they have abandoned ideas for an amnesty for illegal immigrants and now advocate a tougher approach.
But they have bridled at the ad campaign.
'STUPID AND OFFENSIVE'
Business Secretary Vince Cable, a Lib Dem, called it "stupid and offensive", saying he thought it very unlikely to be continued.
"It is designed, apparently, to sort of create a sense of fear in the British population that we have a vast problem of illegal immigration. We have a problem, but it's not a vast one," Cable told the BBC's Andrew Marr Show on Sunday.
He said the Lib Dems had not been consulted about the initiative.
But a spokesman for Cameron, who is on holiday in Portugal, said on Monday that the prime minister didn't agree with Cable's criticism. "No is the short answer," the spokesman told reporters when asked whether he agreed the campaign was "stupid and offensive".
"The pilot is already working. The pilot is about targeting people who are here illegally and giving them the opportunity to leave the country voluntarily rather than be arrested, detained and removed."
The government would review the pilot's success and examine how and whether the campaign could be continued, he added, saying there had been "a great deal of interest" from illegal immigrants in the scheme.
Cameron has ruled with the Lib Dems since 2010, but the two have taken increasingly different positions on issues such as Britain's role in Europe and on reform of Britain's unelected upper house of parliament.
Many traditional supporters of the Lib Dems felt alienated when they struck a coalition deal with the Conservatives, a centre-right party, and have been further disenchanted by what they see as the coalition's "lurch to the right" on immigration and welfare policy.
(Editing by Raissa Kasolowsky)