Donald Trump plans to appear in the witness box to deny allegations that he defrauded thousands of people who signed up for courses at a now defunct college - even while campaigning to be US president.

Earlier this week, a court in New York allowed a multi-million dollar class action lawsuit to proceed against Mr Trump, who is accused of misleading thousands of people who paid up to $35,000 to join the so-called Trump University, learn the billionaire’s real estate investment strategies and meet him in person.

Meanwhile, it has emerged that Mr Trump, the Republican frontrunner, has been named both a defence and prosecution witness in a similar class action lawsuit filed in California by other former Trump University students.

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The controversy surrounding Trump University has been churning for a number of years. But as Mr Trump has achieved frontrunner status in the Republican battle to nominate a candidate for the White House, the tycoon’s rivals have claimed the issue is evidence of Mr Trump unsuitability.

The lawsuit in New York was originally filed in 2013 by the state’s top prosecutor, Eric Schneiderman, and seeks $40m in restitution plus penalties and other costs. The ruling this week also extended the statute of limitations for the claim back to 2007 instead of 2010, Reuters said.

“Today’s decision is a clear victory in our effort to hold Donald Trump and Trump University accountable for defrauding thousands of students,” Mr Schneiderman said in a statement.

Mr Trump has denied the allegations that have been leveled at him. During the Republican debate in Michigan on Thursday night, Mr Trump said that he declined to settle the claims as he believed he was going to win. “Let’s see what happens in two or three years,” he said.

Among those who claim he was defrauded was Roberto Guillo, of Long Island, New York, who said he paid around $1,500 to attend an introductory session with Mr Trump’s staff. He said the event was so inspiring that he was then persuaded to pay $35,000 for the Gold Elite Classes.

Republican presidential candidate Donald Trump (Getty Images)

Mr Guillo told The Independent that he attended four weekend sessions but learned nothing about real estate sales. He never met Mr Trump.

“After the first session I realise I had been scammed,” he said. “I learned absolutely nothing. There were some PowerPoint presentations and a loose-leaf binder full of nothing. They advised us that one way to find properties that were for sale was to drive around the neighbourhood looking for For Sale signs.”

The two lawsuits filed in California involve anywhere up to 5,000 former students of the university, which stopped taking enrollments in 2010.

While a trial date has yet to be set, it could take place in late spring or early summer, according to media reports. The final pretrial conference in the case is scheduled for May 6.

Mr Trump has said he will defend the allegations, even as his campaign for the White House could be entering a crucial stage.

In a statement to The Independent, a spokesperson for the tycoon insisted that “Trump University was a professionally run company which provided students with a valuable and substantive education and the tools to succeed in business and real estate”.