Arthur Titherington, British chairman of the Japanese Labour Camp Survivors' Association, and Keith Martin, of British Civilian Internees, represent 40,000 former prisoners of war and civilian detainees who are each demanding pounds 13,300 from the Japanese government for sufferings during their wartime incarceration.
At the Tokyo District Court today, Frits Kalshoven, Professor of International Law at Leiden University, will give expert evidence supporting their claims that former detainees are entitled to claim individual compensation.
The Japanese government has never denied the claims of ill-treatment, including torture and sexual abuse, but maintains that wartime compensation issues were settled in the 1951 San Francisco Treaty, which exempted it from reparations across the board.
Under the Conservatives, Britain supported that position, but lawyers acting for the plaintiffs are cautiously optimistic that the new government will apply pressure on Tokyo to provide some kind of compensation.
They have already had a meeting with Derek Fatchett, minister of state at the Foreign and Commonwealth Office. "He called us just a few days after taking office, and he said he would try to do as much as he could," said Martyn Day, lawyer for the plaintiffs.
"He asked for a grace period so that he could get on with things quietly behind the scenes, and we've been told that Robin Cook [the Foreign Secretary] raised it yesterday with the Japanese foreign minister in Colorado. The sense I get is that we had a stalemate before, but that the Japanese are more likely to take notice of the new government."
Two years ago, the then Japanese Prime Minister, Tomiichi Murayama, launched a 100 billion yen (pounds 500m) war atonement fund for education and welfare projects in countries whose citizens suffered Japanese mistreatment, but this gesture has been rejected by United States and Commonwealth veterans' organisations, which demand individual compensation.
"Emperor Akihito is coming over to Britain early next year," Mr Day said. "We'll give it until then, and if nothing happens we'll give him a hot reception."