The three former Mau Mau fighters have received support from the Kenyan government, and three academic experts on the uprising, which took place from 1952 to 1960, have made statements in support of the allegations, the BBC said.
In addition, South African Archbishop Desmond Tutu accused British Prime Minister David Cameron of neglecting the country's human rights responsibilities in the case. Britain's unwillingness to make amends, Tutu wrote, was "strongly out of step with many other modern democracies that have been faced with historic allegations of abusive conduct."
The British government has said it was not liable, and the Foreign Office has said it would defend the claim, "given the length of time elapsed and the complex legal and constitutional questions the case raises."
A High Court ruling last year said the claimants -- Paulo Muoka Nzili, Wambuga Wa Nyingi and Jane Muthoni Mara -- had an arguable case.
Lawyers for the claimants alleged Nzili was castrated, Nyingi severely beaten and Mara sexually abused in detention camps during the rebellion.
The claimants are also seeking an apology from the British government.
Kate Middleton recycles dress at movie premiere
Benedict Cumberbatch's dramatic reading of R. Kelly lyrics is just what you need