Bettina Krischbin's paternity suit claimed a stand-in was sent for a blood test in 1983.
... A speaker for the Berlin public prosecutor's office, Michael Grunwald, confirmed on Friday to reporters that the office is investigating claims that McCartney faked a paternity test 23 years ago.
Paul McCartney Under Investigation in Berlin (May 21, 2007) http://www.spiegel.de/international/zeitgeist/0,1518,483950,00.html
...At the top of the piece of paper, there stood “Proof of Identity,” and it dealt with a form that James Paul McCartney, Pass Number PB033834033839, signed back in the beginning of the 1980’s, when his blood was taken. On the identification there was a photo attached, a Polaroid of his face. Bettina Krischbin looked at this face a long time. It is, as stated in the documents, Paul McCartney’s face. She committed that face to memory, went home, and looked at pictures of McCartney in the ’80’s. She found that he looked different at this time than he did on the Polaroid, fuller. “He sent a Double to the test back then,” she said. Her mother sat next to her, smoked, and nodded silently.From F.v.Mutius; B. Jänichen, “Ermittlungen gegen McCartney eingestellt; Berlinerin verliert Kampf um angebliche Vaterschaft des Ex-Beatle,” DIE WELT, 25. Mai 2007:
...She [Bettina] had assembled proof and had gotten ‘two important witnesses,’ who belonged to McCartney’s circle of aquaintances. The world famous singer once supposedly told them, that he had cheated on the blood test...
From Patrick Goldstein, “Berliner Staatsanwalt ermittelt gegen Paul McCartney,” DIE WELT, 19. Mai 2007:
[Recently looking in the files, Bettina] saw a photo together with a signature from the day blood was taken in London. Her verdict: “That is not McCartney. The real McCartney had at this time a much fuller face. The man in the photo looks like McCartney. But he isn’t.” Even the signature is supposedly false. This signature does not hold up to a comparison with the original in the Hamburger Beatles-Museum. In addition: “Friends of mine have looked at and said: a right-handed person wrote that.”Paul is dead - the rotten apple 52 2 (about Bettina)
HTML file with a combination of German/English news reports: http://www.jojoplace.org/Shoebox/McCartney_paternity_case.htm