The North West Development Agency has been found liable to pay £1m to Robert Smith Group, an Inchcape company.
It relates to the sale of a dealership on Liverpool waterfront in 2001. The NWDA paid Robert Smith Group £9.5m for the 4.25-acre property to pave the way for development of the Fourth Grace on the world heritage site.
That project was later aborted, and the NWDA sold the land to developers for less than it paid, who are building residential and office blocks there.
Robert Smith Group argued the NWDA's sale to developers denied it the chance to take extra payment if an overage clause were triggered which would net Robert Smith Group 50% of the value above an agreed level, believed to have been £10m.
It said the land should have been put on the open market to maximise its value.
A hearing ruled the land was worth £12m, meaning the NWDA must pay Robert Smith Group £1m.
Robert Smith Group was bought by Inchcape in 2005.