The StB decided to give him the false identity of Erwin van Haarlem and trained him over several years to become a skilled secret agent with a false - but existing - background. As a - pretended - child of a Dutch mother he had both Czech and Dutch nationality and therefore acquired a Dutch passport at the Dutch Embassy in Czechoslovakia. In 1975 he arrived in Britain and started his spying career for the Czech StB and the Russian Secret Service. Meanwhile, Mrs Joanna van Haarlem found him through the Red Cross and finally was reunited with her alleged son in 1977.
More than ten years she believed to have found her lost son, until he was arrested in 1988 by British Special Branch detectives in his apartment while receiving encrypted shortwave messages from a numbers station. Also, one-time pads, used to decode messages, were found hidden inside soap bars in his apartment. DNA samples later confirmed that he wasn't Joanna's son. Vaclav Jelinek never told his real name during the investigations or at the trial and the spy with no name was sentenced in 1989 to ten year imprisonment. He was released and deported to Prague in 1994. Joanna finally found her real son who had changed his Dutch name in a Czech one at the age of 15. He knew nothing about the misuse of his name by the StB. Jelinek's story is a good example of infiltration under stolen identity during the Cold War.
The complete story of the false identity and how Jelinek was captured can be found on Simon Mason's Shortwave Espionage. It also includes a link to a very intersting two-part radio program (in Dutch) with the story of his mother (part 1) and a 30 minutes interview with Vaclav Jelinek himself (part 2). A 30 minutes BBC Radio 4 program, explaining Number Stations that are used to transmit coded messages on shortwave radio (which also mention Erwin van Haarlem) can be downloaded on Simon's website (6.6 Mb wma file). Very interesting! More on one-time pads and numbers station on my website.
Update 04 Jan 17: BBC Magazine just publish an excellent story on Vaclav Jelinek with many details and photos.