pounds 60m Jubilee Line fraud case collapses.
They had been accused of corruption in connection with the building of the Jubilee Line Underground extension in London.
But after 18-months of the case before a jury, Judge Ann Goddard brought the trial to a stop because of continuing delays.
Afterwards, Attorney General Lord Goldsmith said, 'This decision will cause great public disquiet as it causes me considerable disquiet. Most serious allegations have not in the end been brought to a final conclusion.'
Lord Goldsmith said he had asked the Chief Inspector of the Crown Prosecution Services, Stephen Wooler, to investigate.
The failure to return any jury verdict in the case is expected to herald renewed calls for similar cases to be tried without jurors.
The trial folded after sickness, jury problems, lengthy delays and disruption stopped proceedings to such an extent that a fair trial became impossible.
Judge Goddard formally cleared the six after the prosecution said they would not pursue a retrial and offered no evidence.
The men cleared were
all involved in the Jubilee Line extension project and had all denied corruption. Outside court, one of them, Mark Skinner, said, 'Although I should now feel relief and happiness, I feel only anger.
'Anger at a prosecution which has destroyed my business and tortured my family for over seven years and caused significant damage to my health.
'Anger that no one in a position to do so stepped in and ended what to all reasonable observers had become a farce long ago.'
British Transport Police said, 'The Jubilee Line extension project was at the time the biggest civil engineering project in Europe.
'It was clear that any trial was going to be lengthy.'
Chris Newell, a Crown Prosecution Service director, said, 'The allegations in this case were very serious and it was clearly in the public interest to bring them before a court