UKIP leader Nigel Farage “insulted the intelligence of voters” as he warned yesterday that increasing the minimum wage would see Britain swamped by immigrants.

Speaking on a phone-in BBC Radio 5 Live programme, Mr Farage was asked by a caller whether he would raise the lowest legal pay rate.

“There is a problem with doing that. That is that if you increase the minimum wage, you may actually even attract more migrant labour,” he responded.

“Don’t forget, the minimum wage in Britain is now nine times what it is in Romania. If you increase it even more, people would want to come.”

He made the controversial comments hours after moaning that the audience at the BBC’s Thursday night leaders’ debate was too left-wing.

Hitting back, TUC general secretary Frances O’Grady accused Mr Farage of giving bad bosses another excuse to exploit staff.

“Not content with insulting television audiences, Mr Farage is today insulting the intelligence of voters with these economically illiterate remarks,” she blasted.

“Capping the minimum wage would drive down earnings for low-paid workers across the economy.”

Mr Farage was not the only rightwinger to get himself into hot water yesterday.

Work and Pensions Secretary Iain Duncan Smith sparked fury when he claimed during television interviews that zero-hours contracts should be renamed.

“It should be flexible hours contracts,” he said. “But only 2 per cent of the total workforce have those and they are mostly people like carers, who can’t give direct time, and young people like students, so for them there is a reason for those.”

Labour has pledged to ban the most exploitative zero-hours contracts, but unions have pressed for them to be scrapped altogether.

“We don’t need to rename zero-hours contracts, we need to ban exploitative zero-hours contracts,” said Labour leader Ed Miliband.

“And that’s what the next Labour government will do.”

General union Unite leader Len McCluskey said that zero-hours contracts meant “misery” for workers and their families, leaving them to live “hand to mouth.”

“This insecurity has exploded on David Cameron’s watch, where we have an economy built on shaky jobs and chronic low pay,” he said.The row will generate yet more unwelcome headlines for Mr Cameron, coming as it did on the day that he returned to his boast of having presided over a “jobs miracle” since coming to power.

New joblessness figures published yesterday suggested that unemployment has continued to fall and that a record 31 million people are in work.

The jobless total fell by 76,000 to 1.84 million in the quarter to February — the lowest for almost seven years.

But general union GMB leader Paul Kenny said: “Most of these new jobs are mainly low-skilled, low-paid and zero-hours. Even skilled workers in the UK face being undercut while wages are stagnant or falling in real terms.

“Most workers have seen little or no evidence of any recovery in living standards due to the Tories not promoting real economic growth based on investment and productivity gains.”