An officer from Britain’s FBI carried out searches on an oligarch in hiding during the hunt for spies working for Russian agent Jan Marsalek, The Telegraph can reveal.

The National Crime Agency officer carried out “basic checks” on German Gorbuntsov, an oligarch who is living under 24-hour security protection in the UK after being shot in Canary Wharf in 2012.

Mr Gorbuntsov believes that he was being hunted by Russians who wanted to “finish the job” and kill him.

The details can be revealed after Marsalek’s UK-based spy ring was found guilty on Friday following a three-month trial at the Old Bailey.

The Bulgarians, led by Orlin Roussev, are just one cell used by Marsalek, the fugitive chief operating officer of disgraced payments processing company Wirecard, police believe.

A year-long investigation by The Telegraph has uncovered evidence of the extraordinary double life of the businessman, who was working for the Kremlin while running Wirecard, Germany’s answer to PayPal.

He fled to Moscow when the company collapsed with a £1.6 billion hole in its books and is on Interpol’s most wanted list for fraud.

Before his escape Marsalek had used a network of informants to gain information on “unknown” foreign policy and intelligence in Egypt, Israel and the USA and carry out “background checks” on individuals “with the main foreign services”, according to top secret investigation files seen by this publication.

This included checks on whether a person was wanted or whether they were agents of secret services. Officials fear the network of spies and police officers who carried out these searches spanned a large number of countries.

Named officers and secret agents who carried out searches have been identified in Austria, Italy and Switzerland as well as the UK.