The sanctioned oligarch's lawyers say the warrant was based on false allegations, including claims he funded Russian organised crime, laundered money for Colombian drug cartels and was involved in the murder of two journalists.
"Kompromat" comes from a Russian word denoting damaging and compromising information collected for use in blackmailing, discrediting or manipulating someone, often for political ends.
Fridman's multi-million-pound London mansion was searched in December over an alleged conspiracy to evade British sanctions, conspiracy to defraud the Home Office (interior ministry), conspiracy to commit perjury, and money laundering.
Fridman's lawyer Hugo Keith said in court filings that the NCA has since dropped its inquiry into the alleged conspiracies to defraud and commit perjury, as well as money laundering.
He said the investigation into an alleged conspiracy to circumvent British sanctions - relating to a loan made by Alfa Bank to Fridman's executive assistant - continues.
Fridman is pursuing a legal challenge against the NCA, arguing that the warrant was unlawfully obtained and seeking to have it overturned.
The 59-year-old strongly denies the accusations of wrongdoing, which his lawyers told the court were "gratuitous and unjustified slurs against a businessman of good character".
Keith said in court filings that the allegations, which came from a 15-year-old report published by WikiLeaks in 2012, were "absolutely typical of classic kompromat, damaging and untrue information assembled and used to create negative publicity and to exert influence over the subject".
The NCA's Cathryn McGahey said in court filings that the agency accepts that "failures on its part led to the search of (Fridman's) property and the seizure of items being unlawful".
But Fridman argues the warrant was also unlawfully obtained on other grounds, including that there was no reasonable basis to believe he had committed a criminal offence and because NCA media officers were allowed to enter his home under the warrant.
Fridman, whose net worth is estimated by Forbes magazine at $12.6 billion, has been subject to British and European Union sanctions since March 2022, a month after Russia invaded Ukraine, over his alleged ties to the Kremlin.
Keith said Fridman is currently challenging his designation under both the British and EU sanctions regimes targeting Russia over the war in Ukraine.
(Reporting by Sam Tobin; editing by Mark Heinrich)
By Sam Tobin
