Lord Justice Balcombe, sitting with Mr Justice Popplewell, ruled that the decision not to police Shoreham "on a sufficient scale" had the effect of illegally restricting exports to the European Union.
Shoreham was the scene of bitter conflict in the battle to stop live animal exports. At the height of the protests in January, more than 1,000 police were pitted against hundreds of demonstrators intent on stopping livestock trucks entering the port.
In April, the chief constable, Paul Whitehouse, decided to restrict policing to two days a week or four days a fortnight so that resources could be diverted to fighting crime in the county.
During the first three months of protests, the force spent pounds 3.5m controlling demonstrators at Shoreham. Crime in the county also increased, which the chief constable attributed partly to the diversion of police resources.
Mr Whitehouse said the cost of controlling the protests was having a "significant impact" on his ability to police the rest of the county. "Reducing crime, and the fear of crime, and responding to calls made by the public to the police are the key priorities of Sussex Police. These are fundamental to preserving a peaceful society," he said.
International Traders Ferry Ltd (ITF), a consortium of farmers, traders and hauliers, argued that the police had an obligation to uphold the law and that the chief constable's decision was unreasonable. They also argued that the decision wasa restriction of free trade under the Treaty of Rome.
The court accepted that the decision was a restriction on trade and ordered that Sussex Police should pay ITF's costs. The chief constable was given leave to appeal.
A spokesman for ITF said the verdict was important for the "British livestock farmers whose livelihood depends on continuing a long-established trade with continental Europe". He said urgent consideration would be given to re-establishing the livestock trade through the port.
Assistant Chief Constable Tony Lake said the decision to restrict policing was made to "strike a reasonable balance between the policing demands at Shoreham and the policing needs of the rest of the community."
"To this extent it may be said that the decision was taken in the interests of all the people of Sussex," he added.
John Callaghan, education director at Compassion in World Farming, said the decision would "increase people's frustration and make them even more determined to stop the trade".
Mark Glover of Respect for Animals said there was now a "fundamental gulf between the law and the morals of the British people".Reuse content