Michael Ben-Gad, a professor at City University in London and author of a Treasury-funded report on immigration and fiscal policy, claimed the so-called people's army was flying in the face of “numerous” studies on the matter.
“The bulk of the argument seems to have shifted to the issue of how the immigrants overburden public resources.
"The evidence for this is not presented and belies the work done by [Christian] Dustmann and [Tommaso] Frattini on immigrants – particularly from the EU – and their net contributions to the Exchequer and my own work on immigration and debt,” he said.
“Numerous studies on the effects of immigration on the labour market also fail to find significant effects.”
Ben-Gad also took aim at Ukip's suggestion limiting migration to 50,000 people, which would create net migration out of the UK of around 250,000 people each year.
“Given the rate of natural increase, the population would be shrinking and also ageing very rapidly,” he said.
However, Ben-Gad said the theory of a cap was “far more sensible than the current policy”, highlighting the Australian points system for its emphasis on encouraging immigrants who will contribute to the economy.
What are Ukip's key immigration policies?