Alison and Peter Smithson's seminal archive has been lost to the United States and the Netherlands, the AJ has learned.
Ownership of the collection of drawings by the Brutalist husband and wife team has been divided between Harvard University and the Netherlands Architecture Institute.
Peter Smithson, who died last year, bequeathed most of his collection to Harvard University, where he had taught.
Material relating to Team 10, in accordance with Alison Smithson's wishes, is now owned by the Netherlands Architecture Institute. Additional items remain with the family.
Exhibits from a recent retrospective of the Smithsons' domestic work will go to their new homes once the show completes its tour of Rotterdam, Glasgow and Newcastle.
Simon Smithson, the couple's son, told the AJ the bequest of the 'very well-organised, concise gem' was an outright gift: 'There was a very particular set of circumstances that led us to feeling it was the right thing to do, ' Smithson said. 'The decision was made when the future of the RIBA drawings collection was less certain.'
The curator of the RIBA's drawings collection, Charles Hind, said he was disappointed the archive had left the country.
But he added that the institute already owned a number of drawings gifted during the '70s and '80s, including the Economist Building and Hunstanton School, and a model of the competition entry for Coventry Cathedral - to be included in the V&A's permanent exhibition.
Hind, who has a budget of just £2,500 per year to acquire new work, called on the government to make it more attractive for architects to donate material while they are still alive by offering a personal benefit equivalent to its 'in lieu' scheme for inheritance tax.