The Foreign Office has finally made public the first batch of thousands of "lost" colonial era files believed to have been destroyed.
The documents, which were secretly sent back to the UK when former colonies became independent, shed new light on how British officials ran overseas territories including Kenya, Cyprus and present-day Malaysia.
They also record how colonial administrators planned to burn other classified papers - potentially revealing abuses committed under British rule - before handing power to the new indigenous governments.
The Foreign Office only admitted last year that it held some 8,800 files at Hanslope Park in Buckinghamshire which were "migrated" to Britain from colonies at the time of independence because of their sensitivity.
More than 1,200 of these records were released today at the National Archives in Kew, west London, the first of six tranches in a process due to be completed by November 2013.
A memo in the Kenyan files dated May 1961 sets out the criteria under which papers were to be "migrated".
Then-colonial secretary Iain Macleod said the aim was to ensure no files were passed to a post-independence regime which "a) might embarrass HMG (Her Majesty's Government in Britain) or other governments; b) might embarrass members of the police, military forces, public servants or others eg police informers; c) might compromise sources of intelligence information; d) might be used unethically by ministers in the successor Government."
Dr Edward Hampshire, diplomatic and colonial records specialist at the National Archives, said these guidelines were interpreted "very liberally indeed" by the different colonial administrations, with one even retaining the personnel files for people working as drivers.
Kenyan ministry of defence files state that British officials were told to divide all documents into the categories of "legacy" material, which could be left behind, and "watch" material, which could not.
One memo dated April 1961 - two years before Kenyan independence - noted: "The aim will be to ensure that as much material as possible is left for the unimpaired functioning of the succeeding independent government, and for the proper recording of the past...
"'Watch' material can only be seen by 'authorised' officers. An 'authorised' officer is defined in the draft as a servant of the Kenya government who is a British subject of European descent, and who has been security cleared to see classified documents."
It added: "To obviate a too laborious scrutiny of 'dead' files, emphasis is placed on destruction - a vast amount of paper in the Ministry of Defence secret registry and classified archives could be burnt without loss, and I should be surprised if the same does not apply to the CS's (chief secretary's) Office."
A detailed document explaining how to decide which files should be given "watch" designation added: "There is undoubtedly much old classified material in many offices which is never used, even for reference, and which has no historical significance: this should be burnt by an 'authorised' officer in person."
It stressed that the "very existence" of "watch" material should never be revealed, and advised that officials might need to change page numbers in files to disguise the removal of sensitive papers.
There are similar references to the destruction of classified material in the files relating to Malaya, which became independent in 1957 and joined with three other states to form Malaysia in 1963.
In July 1956, the private secretary to British high commissioner Sir Donald MacGillivray raised the question of what should be done with old papers.
He wrote: "I have been through them and it would seem that some contain items of historical interest in the event of anyone writing a history of the Emergency (the 1948-1960 conflict with communist guerillas) or biography of former high commissioners.
"The others should be dealt with in detail, but I have not time to do this. Would you agree to their disposal as suggested against individual files in the list."
A separate appendix listing the material proposed for destruction includes documents relating to a visit to Malaya by the Duchess of Kent and "law and order" files covering intelligence, the internal security committee and situation reports.
It is not known what happened to these papers, but archivists who have gone through the Malaya files say there are only limited references to the alleged Batang Kali massacre of December 1948, when British troops shot dead 24 unarmed rubber plantation workers.
The "migrated" archives came to light in January last year after four elderly Kenyans brought a High Court case against the UK Government over the alleged torture of Kenyan Mau Mau rebels in British camps in the 1950s.
Only a third of the Kenyan files were released today, but they contain detailed bureaucratic accounts of the policy of seizing the livestock of people suspected of aiding the Mau Mau insurgency.
On January 5 1955 a British district commissioner seized a total of 30 sheep from four members of the Kikuyu tribe who worked on the farm of a Mr SJO Armstrong in the Naivasha district of Rift Valley Province.
A short file on the case reveals that these were all the animals they owned. The action was prompted by suspicions that they had "harboured and fed" a 40-strong Mau Mau gang for a fortnight.
In a line expressing the frustration, and perhaps vindictiveness, of the UK colonial administrators, an official wrote: "Owing to the fact that the Kikuyu labour was totally unco-operative and showed no signs of assisting security forces, native stock was seized."
Tony Badger, a Cambridge University history professor who has been appointed by the Foreign Office as an independent reviewer of the archive's release, acknowledged that there was a "legacy of suspicion" about the documents among journalists and academics.
But he stressed that so far no files have been withheld from release at the National Archives, and significantly less than 1% of the content has been redacted.