On Tuesday the Strasbourg court will decide whether Mr Saunders was deprived of a fair trial six years ago for illegal share-ramping in Guinness's 1986 bid for Distillers.
He is also claiming pounds 5m compensation, which government lawyers called "dishonest" at the Court hearing in February.
At issue are Department of Trade and Industry powers to compel evidence in company frauds and its use in trials.
In 1994, the European Commission on Human Rights voted 14-1 that use of the evidence violated Article 6 of the European Convention.
Government sources expect that, if it does not overturn the ruling outright, the Court may rule the use of evidence unfair, but still find the conviction safe.
In any event, it has no power to quash the conviction.
Official sources say it would fall to Home Secretary Michael Howard to decide whether to refer the case back for the third time to the UK Court of Appeal.
In 1995, however, the Appeal Court found decisively against Mr Saunders - and his three co-defendants, business tycoon Gerald Ronson, stockbroker Tony Parnes and financier Jack Lyons - on the same arguments made in Strasbourg.
A pardon, alternatively, is out of the question. "You won't find anyone here who will say they are sorry Ernest Saunders was prosecuted," one official source said.
Any ruling in his favour would be an embarrassing blow, however. The other three are also preparing appeals, if he wins.
His five-year sentence was halved on his first appeal in 1991. He was released early after claiming he had Alzheimer's Disease, but has since made an amazing - and unique - recovery.