LONDON: British officials burned and dumped documents from colonies in the final years of the empire in a systematic effort to hide their "dirty" secrets, according to files declassified on Friday.

Among the newly released files was a note warning authorities to be careful to avoid a situation similar to India in 1947, when the local press was filled with reports about the "pall of smoke" over Delhi at the very end of the British Raj as officials burnt documents before leaving.

Under " Operation Legacy ", officials in Kenya, Uganda, Malaysia, Tanzania, Jamaica and other former British colonial territories were briefed on how to dispose of documents that "might embarrass Her Majesty's government".

The 50-year-old documents that were finally transferred from the UK Foreign Office to the National Archive in a so-called "migrated archive" show the extraordinary lengths to which the Colonial Office went to withhold information from its former subjects in at least 23 countries and territories in the 1950s and 1960s.

A Colonial Office telegram of 3 May 1961 stated the general guidance for keeping papers out of the hands of newly elected independent governments.

Items should be disposed of if they "might embarrass members of the police, military forces, public servants or others eg police informers; might compromise sources of intelligence" — or might be used "unethically" by incoming ministers.

Among the documents was a memo from London that required all secret documents held abroad to be vetted by a special branch or MI5 liaison officer to ensure that any papers which show "racial prejudice or religious bias" were destroyed or sent home.

The documents also include "destruction certificates" sent to London by colonial officials as proof that they were performing their duties, and letters and memoranda that showed that some were struggling to complete their huge task before colonies gained independence.

Officials in more than one colony warned London that they feared they would be "celebrating Independence Day with smoke".

According to analysts, an elaborate and at times confusing classification system was introduced to protect papers that were to be destroyed or shipped to the UK.

Officials were often granted or refused security clearance on the grounds of ethnicity. Documents marked 'Guard', for instance, could be disclosed to non-British officials as long as if they were from the Old Commonwealth - Australia, New Zealand, South Africa or Canada.

Those classified as 'Watch' and stamped with a red letter W, were to be removed from the country or destroyed. The marking 'DG' was said to be an abbreviation of deputy governor, but in fact was a protective code word to indicate that papers so marked were for sight by "British officers of European descent only".

The British government agreed earlier this year to pay USD 23 million in compensation to more than 5,200 elderly Kenyans who were tortured and abused during the 1950s Mau Mau uprising against colonial rule.

The files released on Friday are the final batch of a collection whose existence was only revealed by the Foreign Office in January 2011 as part of the Kenyan action.