Move to '20-year-rule' for secret papers will cost £52m
The Ministry of Justice says reducing the "30-year rule" for publishing secret government papers to 20 years will cost up to £52m.
The change, which will see government documents released to the public earlier, was announced in February 2010 and will be phased in from 2013.
The MoJ says it wants the changes to be carried out in an "affordable" way.
The National Archive said the move would "provide new insight" into events that shaped Britain's recent history.
The MoJ says the first phase - transferring central government records to The National Archives - will affect 3.3m records and cost between £34.7m and £38.5m over 10 years.
The second phase - transferring local authority records - will cost between £5.6m to £15m.
The changes were prompted by a 2009 review of government transparency by Daily Mail editor Paul Dacre, who was appointed by then prime minister Gordon Brown.
Oliver Morley, chief executive of The National Archives said the move to release documents earlier was a "huge step forward".
"As a result, we can look forward to more records being released on events within living memory, such as the Gulf wars and the 9/11 terrorist attacks, providing the official view of events as they unfolded."
From 2013, two years' worth of government records will have to be transferred to The National Archives at Kew over a 10 year transition period until a new '20-year rule' comes fully into force in 2023.
After this point, the government will revert to transferring a single year's worth of 20 year old records to The National Archives each year.
An extra 45,000 new records could be opened to the public each year during the 10 year transition.