An aide to Donald Trump's 2016 presidential campaign lied to FBI investigators about his conversations with a mysterious Stirling University professor "out of loyalty" to Trump, his defence lawyers have claimed.

George Papadopoulos admits he materially misled the FBI concerning his interactions in 2016 with Professor Joseph Mifsud, who was working at the Scottish university at the time.

Prof Mifsud, a Maltese academic, set up a number of meetings between Papadopoulos and Russian officials and had discussed setting up a summit between then-candidate Trump and Vladimir Putin.

The interactions between the pair also include Prof Mifsud allegedly informing Papadopoulos of "dirt" on Hillary Clinton in the form of "thousands of emails", an accusation the academic denies.

They occurred several months before a huge tranche of Democratic National Committee (DNC) emails were released by Wikileaks following server breaches by suspected Russian hackers in 2015 and 2016.

A new memorandum by Papadopoulos' lawyers refutes a claim by prosecutors working for US special counsel Robert Mueller that their client's lies "substantially hindered" the federal investigation into the Trump campaign's ties to Russia.

The memo comes ahead of Papadopoulos' sentencing on Friday and asks the judge to impose a sentence of probation, as opposed to the jail sentence of up to six months proposed by Mueller's team.

Attorneys Breen & Pugh, representing the former Trump aide, admit in their newly-filed court documents that Papadopoulos' offence was "unquestionably serious" and say he is "ashamed and remorseful" for his actions.

But they add that their client's incriminating conversation with FBI agents investigating Russian interference in the 2016 US election was partly due to being "caught off-guard by an impromptu interrogation".

It goes on to say Papadopoulos first met Prof Mifsud, who "claimed connections to the Russian Government", in March 2016.

"George thought he could utilise him and his connections to help the Trump campaign promote its policy objectives" of improving US-Russia relations, the lawyers claim.

They add that "Professor Mifsud paid young George little attention until learning of his position as one of Trump's foreign policy advisors", which was announced later that same month.

Their client was "giddy" at the recognition he received from Trump, who described Papadopoulos in an interview as an "excellent guy".

The memo adds that the "28-year-old George witnessed his career skyrocketing to unimaginable heights" upon taking the new role.

Prof Mifsud then arranged a meeting in London where he allegedly introduced a Russian woman to Papadopoulos called Olga who he falsely claimed was President Putin's niece.

The memo states: "Professor Mifsud and Olga led George to believe that they had the wherewithal to set up a meeting between the Trump campaign and Russian government officials."

At the end of March, Papadopoulos says he brought up the possibility of a meeting between Trump and Putin at a Trump campaign meeting, at which the presidential candidate "nodded his approval", his lawyers allege.

Prof Mifsud is also said to have put Papadopoulos in contact with a man called Ivan Timofeev, who had links to Russia's ministry of foreign affairs.

However, the former Trump aide denies ever informing anyone on the campaign of what he alleges Prof Mifsud told him in London over breakfast on April 26, 2016: that the Russians had "dirt" on Trump's rival, Clinton.

On the other hand, he also admits in the memo that he did inform the Greek foreign minister in May 2016 of the "dirt" on Clinton, "days before President Vladimir Putin travelled to Greece to meet with Greek officials".

He is also known to have shared this information the same month with Australia's top diplomat in the UK, Alexander Downer, whose subsequent tip-off prompted the launch of the FBI's investigation into the Trump campaign's ties to the Kremlin.

He divulged the details to Mr Downer after a night of "heavy drinking" in London, it was reported.

After he was taken in for questioning by the FBI in January 2017, Papadopoulos was quizzed at length by investigators about his dealings with Prof Mifsud, the Trump campaign and other actors.

The memo states: "George found himself personally conflicted during the interrogation as he felt obligated to assist the FBI but also wanted to distance himself and his work on the Trump campaign from that investigation.

"Attempting to reconcile these competing interests, George provided information he thought was important to the investigation while, at the same time, misleading the agents about the timing, nature, and extent of his contacts with Professor Mifsud, Olga, and Ivan Timofeev.

"In his answers, George falsely distanced his interactions with these players from his campaign work."

It adds: "In his hesitation, George lied, minimised, and omitted material facts.

"Out of loyalty to the new president and his desire to be part of the administration, he hoisted himself upon his own petard."

Prof Mifsud quit his post at Stirling in November last year around three weeks after his identity was revealed following the original indictment filed by Mueller against Papadopoulos.

In media interviews shortly after the story first broke late last October, the academic protested his innocence, saying that while he helped Papadopoulos network with contacts, he had nothing to do with "dirt".

"I never got a penny from the Russians, my conscience is clean," he told an Italian newspaper.

Prof Mifsud's present whereabouts are unknown, after he most recently failed to show up at an Italian court on charges of unjustifiably inflating salaries at a university in Sicily in 2010.

Buzzfeed reported remarks by prosecutors in Palermo describing the professor as a "ghost" and a "peculiar subject".

As STV News revealed last year, at the time of his interactions with Papodopoulos in the spring of 2016, Prof Mifsud was working for Stirling University as a part-time professorial teaching fellow.

Emails obtained by STV also showed that university management had boasted to staff in the politics department of the academic's links to Vladimir Putin, around the same time as his meetings with the Trump aide.

Prior to being directly employed at the Scottish university, Prof Mifsud ran a school called the London Academy of Diplomacy which was affiliated with Stirling between 2014 and 2016.

Stirling has faced scrutiny over its involvement with both Prof Mifsud and the London academy, amid concerns over the Maltese national's academic credentials and his personal relationship to members of university management.

The university maintains Prof Mifsud was hired, with appropriate due diligence carried out, due to his portfolio in "international affairs and diplomacy reflecting his academic and professional background in this field".

Former foreign secretary Boris Johnson was also quizzed about the professor after they were pictured together at a fundraising dinner in Berkshire last October.

Johnson denied having "knowingly met" the academic.