Slater counter-sued Craig for statements he made in a leaflet sent out to 1.6 million households around the country in 2015.
Justice Toogood found that Slater did defame Craig, by making untrue statements about him.
But not all of Craig's defamation claims were successful; Justice Toogood dismissed Slater's counter-claim.
Craig then took the case to the Court of Appeal in March. It released its ruling today.
It has found the High Court was incorrect in some areas, including failing to award damages and costs to Craig.
He can now go back to the High Court to have that re-examined.
"We remit damages and costs in the High Court for redetermination in that court in light of the terms of this judgment."