An estimated 160,000 people were detained during the insurgency
Veterans of Kenya's independence struggle are launching a compensation claim against the UK for alleged atrocities by the British army.
Lawyers for Mau Mau veterans said they had documented 40 cases of torture, including castration, sexual abuse and unlawful detention.
A spokesman for the veterans in Nairobi said they were confident of success.
The UK government has said the claim is invalid because of the time that had lapsed since the alleged abuses.
Five elderly Kenyans - three men and two women - detained during the 1950s insurgency are the lead claimants in the reparations case to be lodged at the High Court in London on 23 June.
The case is being brought by the Mau Mau War Veterans' Association and the Kenya Human Rights Commission, through London law firm Leigh Day & Co.
It is not the first compensation claim brought by Kenya's former independence fighters against the British government.
Tom Kagwe, deputy executive director of the Kenya Human Rights Commission, told Sunday's news conference in the Kenyan capital: "The actual number of Kenyans who suffered this barbaric treatment at the hands of British officers in fact runs into the thousands."
Seventy-nine year old Gitu wa Kahengeri, a spokesman for the Mau Mau War Veterans' Association, told the BBC's Focus on Africa programme: "The colonial government had treated the people of Kenya inhumanly.
"Many women were raped, many women were inserted bottles of hot water into their private parts."
The British foreign office said in a statement: "The Mau Mau issue remains a deeply divisive issue within Kenya which historians continue to debate.
"The emergency period caused a great deal of pain for many on all sides, and marred progress towards independence. It is regrettable this was not achieved without violence."
Historians say the Mau Mau movement helped Kenya achieve independence in 1963.
It started in the European-owned farmlands in the Kenyan highlands in 1952.
Mau Mau fighters launched attacks on white settlers, spreading terror through the white farming community.
The Kenya Human Rights Commission has said 90,000 Kenyans were executed, tortured or maimed during the crackdown, and 160,000 were detained in appalling conditions.