The three had reportedly lived in the UK for a number of years, at different locations.
Three Bulgarian citizens living in England have been charged with possessing false identity documents, police said.
The trio - Orlin Roussev, 45, Bizer Dzhambazov, 42, and Katrin Ivanova, 32 - were among five people first arrested in February, and were taken into custody after they appeared last month in the Central Criminal Court in London.
The trio is suspected of working for Russian security services, British media reports.
The charges allege the three had false documents among 34 pieces of identification in their possession.
The BBC said documents, including passports and identity cards, were from the UK, Bulgaria, France, Italy, Spain, Croatia, Slovenia, Greece and the Czech Republic.
Counter-terrorism detectives arrested the three with two others on suspicion of an offense under the Official Secrets Act 1911, which criminalises spying. That investigation continues.
The other two arrested, a 31-year-old man and 29-year-old woman, both from London, were released on bail and are due in court next month.
No pleas have been entered for the three people charged. Their next court date has not been set.
British media reports the three had been living in the UK for several years.