Charlie Gilmour was one of thousands of students who demonstrated in December against rising university tuition fees. He was among a group that broke away from the main demonstration and attacked the convoy carrying Prince Charles and his wife, Camilla.
Gilmour also was photographed hanging from a Union flag on the Cenotaph, a memorial to British war dead.
The 21-year-old Cambridge University student pleaded guilty to violent disorder but challenged the length of his sentence.
But the Court of Appeal said Friday that the sentence was neither “manifestly excessive (nor) wrong in principle.”