Donald Trump threatened his high school and college with legal action in order to prevent them releasing his exam scores, according to explosive testimony Michael Cohen is due to deliver before Congress.

Mr Cohen, the US president’s former lawyer and personal fixer, will tell the House oversight and reform committee on Wednesday how his then client directed him to send letters warning Mr Trump’s schools against releasing his grades.

The revelation is part of a larger picture Mr Cohen plans to sketch of Mr Trump as “a racist, a conman, and a cheat” who, he will claim, knew his campaign was communicating with WikiLeaks in order to damage his 2016 presidential rival Hillary Clinton.

“When I say conman, I’m talking about a man who declares himself brilliant but directed me to threaten his high school, his colleges, and the College Board to never release his grades or SAT scores,” Mr Cohen will say, according to a transcript first obtained by the New York Times.

“As I mentioned, I’m giving the committee today copies of a letter I sent at Mr Trump’s direction threatening these schools with civil and criminal actions if Mr Trump’s grades or SAT scores were ever disclosed without his permission.”

He will continue: “The irony wasn’t lost on me at the time that Mr Trump in 2011 had strongly criticized President Obama for not releasing his grades.”

Mr Trump branded Barack Obama a “terrible student” in an interview nine years ago with the Associated Press, in which he pressured the former president to release his academic records.

Mr Cohen, who once said he would take a bullet for Mr Trump, will tell lawmakers how he is “ashamed” over his efforts to “protect and promote” his former boss.

“I am ashamed because I know what Mr Trump is. He is a racist. He is a conman. He is a cheat,” he will say.

“He was a presidential candidate who knew that Roger Stone was talking with Julian Assange about a WikiLeaks drop of Democratic National Committee emails.”

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Last summer, Cohen pleaded guilty to charges of tax evasion, bank fraud, and campaign finance violations in relation to hush money payments made to two women, Stormy Daniels and Karen McDougal, on the eve of the 2016 election.

He also pleaded guilty to a separate charge by brought by Robert Mueller’s office that he lied to Congress about discussions over the construction of a proposed Trump Organisation skyscraper in Moscow – referred to in court documents as the “Moscow Project”.

He was sentenced to three years in jail and is due to start his sentence shortly.