The Technology and Construction Court threw out the retailer's claim for compensation and ordered it to pay ICL, now part of Fujitsu Systems, £1.2m, after ruling that the Co-op and the supplier had failed to agree a valid contract.
But in documents lodged in court the Co-op claimed that the original trial judge, Richard Seymour, "invented" evidence, drew conclusions that neither side had argued in court and made "unwarranted" personal attacks on Co-op witnesses and its legal team.
The retailer has replaced its original legal team, London law-firm DLA and barrister Richard Mawrey, following the judge's criticism. Law firm Ashurst Morris Crisp and barrister Christopher Carr will now represent the company in the appeal, which is expected to be heard later this year.
"Given the comments made by the judge, it would not have been credible for us to field the same team," the Co-op said. "Having said that, they have detailed knowledge of the case, so we are retaining them in an advisory capacity."
The Co-op pulled out of the multimillion-pound project with ICL to harmonise store IT systems across the group after failing to persuade ICL to accept financial penalties for late delivery. The Co-op claimed ICL had failed to meet deadlines and had delivered poor quality code.
However, the judge accused senior IT staff from the Co-op of lying to the court to support their case and claimed they had conspired to plot the downfall of ICL, which was developing its Global Store retail software for the firm.
The Court of Appeal has decided to hear the case, despite suggestions by the original trial judge that there were no grounds and that an appeal would be "impertinent."