LONDON: The Indian High Commission in London has handed over the extradition request documents for fugitive diamantaire Nirav Modi , wanted in India as a prime accused in the $2 billion loan fraud scam at Punjab National Bank, to the UK Central Authority, according to official sources here.

The unit within the UK government's Home Office will now process the request, which falls under mutual legal assistance requests, to assist in criminal investigations or proceedings, before an extradition warrant can be issued against Modi.

The whereabouts of the fugitive jeweller remain unknown, but the Indian government had been informed by the UK's Crown Prosecution Service (CPS) in June that it can initiate extradition proceedings despite the uncertainty.

In a written reply to a question in the Rajya Sabha, Minister of State for External Affairs V K Singh had said earlier this week that an extradition request for Nirav Modi "has been sent by a Special Diplomatic Bag to the High Commission of India (HCI), London, for onward transmission to the UK authorities".

Official sources in London confirmed that the documents had soon after been submitted to UKCA this week, setting the extradition process in motion. India falls under the Category 2 set of countries within the UK's Extradition Act 2003, which require a decision by UK courts as well as the country's home secretary.

According to information available in the UK, Modi arrived in London earlier this year on an Indian passport. The UK government was informed about the revocation of that particular passport via a formal Note Verbale from the Indian authorities on February 19, following which the UK Home Office indicated that the businessman had already entered the UK on that travel document but there was no record of him exiting the country.

It later emerged that the 47-year-old was able to travel in and out of Britain at least four times since his passport was cancelled by the Indian authorities in February, having visited the UK, France and Belgium among some of the countries in the past few months.

During his stay in London he was reportedly living in the heart of the city above his jewellery boutique called "Nirav Modi" on Old Bond Street, which has since closed down. His last reported exit from the UK was on a flight to Paris at the end of March.

Modi and his uncle, Mehul Choksi, are the main accused in the PNB scam and they both left India before the details of the fraud came to light on January 16. While it has now emerged that Choksi has taken citizenship of the Caribbean island of Antigua, his nephew's location remains unclear.

The Interpol has issued two Red Corner Notices against Modi and the Indian government has also written to several European countries seeking assistance in tracking down Modi.

If the jeweller is traced in Britain, the extradition request to the UK government could follow a similar course as the case of embattled liquor tycoon Vijay Mallya, who is fighting extradition to India on fraud and money laundering allegations amounting to an estimated Rs 9,000 crores.

The 62-year-old Mallya had voluntarily submitted for arrest to Scotland Yard at a London police station in April last year after an extradition warrant was issued.

The next hearing in Mallya's extradition case at Westminster Magistrates' Court in London is scheduled for September 12.

India and the UK have an extradition treaty, signed in 1992 and in force since November 1993. So far only one successful extradition has taken place from the UK to India under the treaty - that of Samirbhai Vinubhai Patel, who was sent back to India in 2016 to face trial in connection with his involvement in the post-Godhra riots of 2002.

Besides Mallya, there are around six Indian extradition requests pending in UK courts involving fugitives Sanjeev Kumar Chawla, Rajesh Kapoor, Tiger Hanif, Atul Singh, Raj Kumar Patel and Shaik Sadiq, based on a government statement made in the Rajya Sabha last year.

