Pakistan Tehreek-i-Insaf Chairman Imran Khan avoided taxes via an offshore company, Pulitzer prize winning journalist Frederik Obermaier said in a tweet on Monday.

"Just for the record: Mr Khan avoided United Kingdom taxes via an offshore company," Obermaier, who was also a part of the team that unearthed the Panama Papers, said.

Niazi Services, the offshore company mentioned in the tweet, is already under discussion in an ongoing case before the Supreme Court seeking the disqualification of the PTI chief and party secretary general, Jahangir Tareen, for non-disclosure of assets, existence of offshore companies and allegations that the party received foreign funding.

The court had sought a money trail for Imran Khan's Draycott Avenue apartment in London, which he claimed to have purchased through Niazi Services.

In documents submitted to the court, the PTI chief maintained that in 1984, had had mortgaged the 165 Draycott Avenue property in London’s swanky Chelsea neighbourhood — a one bedroom apartment — through the Royal Trust in the name of Niazi Services, which was purchased for around 117,500 pounds.

Explore: No salary records of Imran’s county career, SC told

The 20-year mortgage included an initial down payment to the Royal Trust of 61,000 pounds, which was paid for by Khan’s earnings playing cricket for Sussex and out of his savings. In addition, he received $75,000 through the Kerry Packer series from 1977 to 1979, Khan's application said.

The Royal Trust mortgage contract was created in April 2, 1984, where the interest rate was fixed at 13.75 per cent per year for the next five years. The mortgage on the principal amount was paid off by Khan in 68 months, by Dec 1989, thus redeeming his mortgage, according to the documents.

This amounted to 55,000 pounds, which mostly came from earnings from Sussex, while interest payments were made from money received while playing for New South Wales, Khan claimed.

The PTI chairman in a statement submitted before the court clarified that his London flat was not mentioned in his Pakistani tax returns but was declared through a tax amnesty scheme in the year 2000 and subsequently appeared in his election nomination papers for 2002.

Read more: London flat was declared under 2000 tax amnesty scheme: Imran's lawyer

Khan's counsel Naeem Bokhari told the court that to his client's knowledge, foreign income was non-taxable in Pakistan, which is why taxes were not paid on his flat.

The cricket-turned-politician had declared the property via a tax amnesty scheme, which meant that it did not need to be declared in yearly tax returns, Bokhari said.

Interest in Pakistani politics

Earlier this year, Nawaz Sharif's daughter, Maryam Nawaz, was schooled by Frederik Obermaier and fellow Pulitzer-winner Bastian Obermayer‏ after she tweeted that "Panama is crap".

"Sorry to tell you [but the] Panama papers ARE about corruption," Bastian responded, adding: "Journalism isn't about bringing down a government. It's about telling the truth."

Backing his colleague up, Frederik tweeted to Maryam saying, "Trashed in the rest of the world? In case you missed it: approximately 150 investigations [and] audits... in nearly 80 countries."

Following the Panama Papers leaks, the Sharif family and its finances were the subject of a year-and-a-half long Supreme Court case and accompanying probe spearheaded in part by PTI's Imran Khan, leading to the disqualification of Nawaz Sharif from the post of prime minister on July 28 by the Supreme Court on an unrelated charge.

The corruption allegations against the family have been deferred to accountability courts.