The men were convicted in the first major criminal trial in nearly 400 years to be heard without a jury in Britain, The Times of London online reported.
John Twomey, 62; Peter Blake, 57; Barry Hibberd, 43; and Glenn Cameron, 50, were convicted in London's Central Criminal Court and were to be sentenced later for targeting a Menzies World Cargo warehouse in 2004.
The four were found guilty of robbery and having a firearm with intent to commit robbery.
The defendants' three previous trials ended after a defendant fell ill at the first trial, the jury became deadlocked over a verdict at the second and allegations of jury tampering emerged in the third.
The combined trials cost taxpayers an estimated $45 million, The Times reported.