The RIBA has missed out on a stunning archive of architectural drawings by Sir John Soane.
The collection, belonging to Claremont House in Esher, also includes artwork by 'Capability' Brown and Henry Holland.
However, the Department of Culture, Media and Sport (DCMS) dashed the hopes of the RIBA Library by allocating the 52 drawings to the National Trust.
Tim Drewitt, RIBA honorary librarian, said: 'We were extremely interested in the collection but the government gave it to the National Trust, mainly because the trust owns Claremont House.'
The drawings were part of a batch of material taken through the 'acceptance in lieu' scheme. This allows people to transfer historic works into public ownership to off-set inheritance tax; the Claremont collection is worth £227,500 in tax.
Other recent objects coming into the public realm include a 17th-century corset and three portraits by Nancy Sharp, one of which is of architectural historian John Summerson. This went to Sir John Soane's Museum, which Summerson curated for almost 40 years.
The British Architecture Library is still finalising the addition of work by the late Denys Lasdun and Leslie Martin to its archive.
Lasdun is famous for the National Theatre on London's South Bank. Martin's work included the Royal Festival Hall, also on the South Bank.
Meanwhile, Drewitt said he was busy digitalising the library's photo collection and advancing its IT.
'We are not a dead organisation of musty people wearing leather patches on our jackets, ' he said.