A businessman who said that the public shouldn’t complain about migrants undercutting British workers and taking on jobs for less money is to lead the campaign to keep the country in the EU.

It is to be revealed at an event on 12 October that Lord Stuart Rose, the former chief executive of Mark and Spencer, is to be the chairman of the In campaign.

But the appointment is likely to be leapt upon by opponents because of his robust views on the free movement of labour.

Two years ago the Conservative peer said he had little sympathy with people who complained that jobs were being taken by workers from Bulgaria and Romania who were prepared to work for less money. “I’m a free-market economist; we operate in a free market,” he told Sky News. “If these people want to come here, and work the hours they are prepared to work for the wages they are prepared to work for, then so be it.”

Lord Rose said he believed that pulling out of the European Union would risk Britain’s prosperity. “Most people will make a hard-headed, practical calculation in the coming referendum on what is best for the British people,” he said.

“I believe that Britain is stronger in Europe. The choice is between remaining stronger, safer and better-off inside Europe, or taking a leap into the unknown, risking our prosperity, threatening our safety, and diminishing our influence in the world.”

The announcement comes as the two anti-EU campaign groups traded blows. The Vote Leave campaign has been launched with the backing of some of the biggest political donors in the country as well as prominent figures from the world of business and MPs. But it faces a battle with the rival group, Leave EU, launched by the Ukip backer Arron Banks, to win the designation of the Electoral Commission as the official Out voice.

Whichever group comes out on top will enjoy advantages including higher spending limits, campaign broadcasts and public funding of up to £600,000. But while Ukip’s leader Nigel Farage pledged to work “hand in hand” with Leave EU, the party’s only MP, Douglas Carswell, has come out firmly for Vote Leave.