The Metropolitan police have handed a file on the year-long cash-for-honours investigation to prosecutors.
The Crown Prosecution Service (CPS) will now review the 216 page report and decide what, if any, charges are to be brought.
Met officers interviewed 136 people as witnesses or suspects during the course of the investigation. One was the prime minister Tony Blair, who was interviewed as a witness, making him the first sitting prime minister to be interviewed in Downing Street.
Three people remain on bail and will await the CPS' decision. Labour's chief fundraiser Lord Levy has been arrested on charges relating to the Honours (Prevention of Abuses) Act 1925 and laterally on suspicion of attempting to pervert the course of justice.
Number Ten chief of staff Jonathan Powell has been arrested on charges relating to the 1925 Act and Mr Blair's aide Ruth Turner has been arrested on similar charges and also on suspicion of perverting the course of justice.
For a prosecution to go ahead, the CPS must decide there is a reasonable chance of success and if it is in the public interest.
The final decision to prosecute rests with the attorney general Lord Goldsmith. His involvement has proved controversial, given that he was appointed by the prime minister. Nevertheless, Lord Goldsmith insists his decision will be based on legal facts.
The file will first be examined by Carmen Dowd, head of specialist crime at the CPS. Prosecutors have also hired David Perry QC to examine the evidence and see if any charges could be brought.
Normally Ms Dowd's decision would be approved by the director of public prosecutions Ken Macdonald, but he has announced he will step aside from the case due to his professional links with the prime minister's wife Cherie Blair.
This is the 12th submission the Met have handed to the CPS and the two organisations have worked closely together throughout the investigation.
The cash-for-honours inquiry was launched following a complaint by the SNP, after it emerged four businessmen loaned the Labour party money for the 2005 election campaign and were subsequently nominated for peerages.