A recreation of an anti-war protest camp in Parliament Square will have a permanent home at the Tate.
State Britain, Mark Wallinger's 2007 reconstruction of Brian Haw's long-running, one-man peace camp against the Iraq war, has been given to the gallery by the British artist for its collection.
Haw, who died in 2011 aged 62 of lung cancer, spent 10 years camped outside Parliament fighting off attempts to force him to move while protesting against British military action in Iraq and then Afghanistan.
Wallinger won the Turner Prize for the £90,000 installation, which painstakingly recreated everything from the tarpaulin shelter and tea-making area to messages of support and hand-painted placards from Haw's 40-metre encampment.
An artist's protest letter to then-Education Secretary Michael Gove has also been acquired by the gallery.
Bob and Roberta Smith - the pseudonym of artist Patrick Brill - created a stream-of-consciousness "letter" to Mr Gove, featuring black text on a white background, to vent his concerns about the place of arts in the curriculum.
The museum also announced that it has acquired the earliest work by a female artist to enter the collection, Portrait Of An Unknown Lady (1650-5) by Joan Carlile, who was the first woman in Britain to work as a professional portrait painter in oil.
Tate Britain director Alex Farquharson said State Britain is "highly charged" and a "meticulous reconstruction" of the original, adding: "We have a responsibility to build the national collection of British art on behalf of future generations. This is not the result of a wild spending spree."