Sir Vince Cable has accused Theresa May of being obsessed by an “arbitrary” target to cut immigration, warning that her “posturing” has fuelled a dangerous and misleading impression that the issue is “out of control”.

The new leader of the Liberal Democrats attacked the Government’s goal of reducing net immigration below 100,000 a year as “amateurish,” “absurd” and having “malign consequences” including economic and social damage.

Writing in The Independent, Sir Vince argued that the tough line on immigration on which Ms May has built her career has now backfired because she has failed to cut net migration, which is still running at 248,000 a year.

Sir Vince, the former Business Secretary, lifted the lid on his battles with Ms May during the 2010-15 Coalition, when she was Home Secretary.

He claimed she delayed Lib Dem plans for exit checks at borders which would have ensured much more accurate figures on the number of people leaving the UK than the “laughably inaccurate” airport survey used until recently.

He said her crackdown on overseas students saw 48,000 wrongly and illegally sent home.

Although his Department for Business “stopped the more draconian controls”, large numbers of foreign students were deterred from coming to the UK, depriving British firms of engineers and scientists.

“One of Britain’s most successful export industries – higher education – was, and is, being sacrificed by Theresa May’s Home Office in pursuit of the immigration target,” he said.

The Lib Dem leader respected Ms May as a formidable cabinet opponent, but believes her narrow obsession with the headline immigration figure clouded her judgement.

David Davis suggests immigration target won't happen during next parliament

He thinks Ms May is acting today as if she were still Home Secretary instead of taking a wider cross-government view of the economic and social impact of immigration that any prime minister should.

Sir Vince, who will make immigration a key theme of his leadership, announced his support for the Drop the Target campaign run by The Independent and Open Britain, the successor to the Remain campaign in last year’s referendum.

Arguing that the government target to reduce net immigration to the tens of thousands has “no remaining credibility”, he said: “The figure seems to have been plucked out of the air with no evidence base and with no realistic prospect of meeting it.

“The most damaging consequence of choosing a target in this amateurish and arbitrary way, and then hopelessly missing it year after year, has been a deepening public cynicism feeding the narrative that immigration is ‘out of control’.”

Sir Vince accused Ms May of causing “real anguish” for the three million EU citizens living in the UK, by using them as “bargaining chips” in the Brexit negotiations rather than giving them an unqualified guarantee to remain.

He warned that attempts to curb recruitment overseas to meet the target will “lead to economic slowdown as production is disrupted”.

A Conservative spokesman said: “The Liberal Democrats are desperately trying to re-write history in an attempt to cover up for the fact they have no credible policy on immigration and are completely out of touch with the British people on this issue.

“We are putting forward sensible measures that mean we can take advantage of Brexit, gain control of our immigration system and reduce numbers while providing firms with the workforce they need.”

The former Business Secretary during his first speech as Lib Dem leader earlier this month

Ministers insist the UK will continue to be “an open and tolerant country that welcomes the best and brightest”.

They point out that since 2010, there has been a 47 per cent rise in international students applying to Russell Group universities.

Brandon Lewis, the immigration minister, said it remained the Government’s “long-term aim” to bring immigration down to “sustainable levels”, but could not say when that would be achieved or whether it would happen in the current five-year parliament.

He told BBC Radio 4: “[It is] our determination to see net migration fall to sustainable levels and we think that is around tens of thousands – it’s something we’ve had and continue to have as our long-term aim.”

He added: “If this was an easy thing to do we would have already done it. We cannot, people know, control our net migration levels fully until we leave the EU.”

Ministers argue that a review of EU migration after Brexit by the independent Migration Advisory Committee will ensure the long-term approach demanded by Sir Vince.

Alison McGovern MP, a leading supporter of Open Britain, said: “It’s hugely encouraging to see MPs from different parties backing this important campaign.

“MPs from across Parliament need to make clear to the Government their opposition to the damaging and divisive immigration target.

“By rightly seeing the need for a Brexit transitional arrangement, ministers have effectively conceded that the target is unachievable in this Parliament.

“They should be straight with the public, drop the target, and acknowledge the vital work EU citizens do in our businesses and our NHS.”

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