Eurotunnel is to be compensated by the UK and French governments for losses it suffered because of the Sangatte refugee camp in northern France.
Refugees tried to walk through the tunnel or sneak onto trains
The Channel Tunnel operator says refugees at the camp trying to use the tunnel to get to Britain cost it £30m.
The Permanent Court of Arbitration in the Hague ruled that the governments failed to ensure normal conditions of order and public safety around Calais.
The tribunal is to set a timetable for deciding how much compensation is due.
The Red Cross camp was less than an hour's walk from Eurotunnel's terminal.
It was closed in 2002, following years of criticism that the camp was being used as a base for illegal immigrants trying to get into the UK.
In 2004, Eurotunnel estimated that it had spent £17m on extra security and lost £13m of revenue from delays and cancellations.
A Home Office spokesman said "We are disappointed with the result of this case and are currently studying the detail of the determination."
"Intrusions of illegal migrants into the terminal at Coquelles dramatically reduced following the closure of the migrant centre at Sangatte in 2002 and the introduction of UK border controls at French ports," he added.