No-one has ever been prosecuted for the deaths even though evidence showed the detainees at Hola detention camp were clubbed to death by prison warders after they refused to work.
But the documents reveal that British officials attempted to blame the deaths on "drinking too much water" rather than violence.
One of three elderly Kenyans, who last month won a High Court ruling to sue the British Government for damages over torture, claims he was beaten unconscious during the incident in March 1959.
The prison camp was one of many in which suspected rebels were detained, often in dire conditions, the files released by the National Archives showed.
Concerns about treatment were raised as far back as 1953, when the then Solicitor General described abuses as "distressingly reminiscent of conditions in Nazi Germany or Communist Russia", according to one document.
Shortly before the Hola deaths, a plan had been drawn up allowing prison staff to use force to make detainees work if they refused, the files showed.
But one prison officer, Walter Coutts, told the inquest into the Hola deaths that the detainees either "willed themselves to death or had died because they drank too much water".
Two weeks after the massacre, Mr Lennox-Boyd, a Cabinet minister, wrote to the Governor of Kenya stating he would tell Parliament that the detainees died "after drinking water" and that "autopsies revealed that there were injuries on the bodies which might have been caused by violence".