The fullest account yet of a massacre which took place during the Mau Mau rebellion in Kenya in the 1950s, has been given in Foreign Office documents released by the National Archives.
Eleven Kenyans were beaten to death by prison warders at the Hola detention camp. Dozens more were injured.
There were no prosecutions after the Hola massacre.
Survivor Wambugu Wa Nyingi is one of three Kenyans currently suing the UK government for alleged torture.
The newly declassified documents reveal that in 1958 there were serious problems of discipline at the Hola detention camp near Garissa, eastern Kenya, where Mau Mau suspects were being held.
Detainees complained of being treated "like slaves" while carrying out enforced work on an irrigation scheme. Another grievance was over their diet, which they claimed was responsible for many diseases.
On 3 March, 1959, 11 Kenyans died at Hola. Initial public statements suggested the men had been poisoned by contaminated water.
But three days later, Kenya's governor, Evelyn Baring, wrote to the secretary of state for the colonies, Alan Lennox-Boyd, saying preliminary reports had been "misleading".
"(The) result of first three autopsies is that in each case, death was due to violence", said the governor's telegram to London.
The colonial secretary began to demand daily updates from Nairobi.
"I am sure you will understand my anxiety to have fullest possible information by morning of Tuesday March 10 at the latest. Please let me know what further publicity you propose and whether or not disciplinary proceedings or charges are likely to follow from these findings", wrote Mr Lennox-Boyd.
On 9 March, Mr Baring sent this telegram to London: "The injuries are reported to be consistent with being caused by heavy sticks or batons and/or boots".
In Parliament, the colonial secretary was to face awkward questions about whether the government had, in effect, had a plan authorising the unlawful use of violence against detainees in Kenya.
Mr Lennox-Boyd wanted to establish how many British officers and African warders were alleged to have been implicated in the assaults on detainees at Hola.
The governor replied that two European prison officers had been in charge. He said there were also 40 warders with batons, supervising the prisoners at work, and a special platoon of 51 warders as a riot squad, equipped with batons and shields.
As an inquest got under way in Nairobi in March 1959, Mr Baring sent another cable to London about the proceedings: "Government Chemist told of examination water from cart and stomach contents. Both negative, no poisonous substances found".
The hearing on 26 March saw the Hola camp commandant, Michael Sullivan, giving evidence.
The telegram from Government House in Nairobi to the Secretary of State read: "Sullivan proved very bad witness. An unintelligent man with poor education. He would not directly answer questions but took refuge in rambling statements couched in flowery officialese. Magistrate not impressed".
Summing up the magistrate's findings, Mr Baring told London: "Broadly, death was caused by shock and haemorrhage due to multiple bruising caused by violence".
He went on: "Evidence as a whole so conflicting and unreliable that impossible to be certain of exact happenings on March 3 when things got out of control of one man"..... "Not a single witness of Hola Prison Staff, warders or detainees made any real attempt to tell truth".
In May 1959, the colonial secretary wrote again to Mr Baring: "Public opinion is extremely sensitive on Hola problem.... I am sure you will agree we should try to let this unhappy incident drop out of sight as soon as possible".
Mr Wa Nyingi and his two fellow claimants won a legal case in the UK in October to make a claim against the British government.
The government accepts that the colonial administration tortured detainees, but denies liability .