A new archive of Lucian Freud’s sketchbooks, drawings and letters has been permanently allocated to the National Portrait Gallery.

The National Portrait Gallery, which in 2012 staged the Lucian Freud Portraits exhibition, the gallery’s most visited ticketed exhibition, plans to make the archive, which has never been published or exhibited, accessible to the public from summer 2016.

Also included in the archive is a collection of childhood drawings by Freud when he was living in Germany, before his family fled to England in 1933 when Hitler came to power. The drawings were preserved by his mother, many are annotated by her with a date and place and they reveal much about the family life of the Freuds.

The National Portrait Gallery acquired the archive through the Arts Council's Acceptance in Lieu scheme, which enables taxpayers to transfer important works of art and other heritage objects into public ownership. The Freud archive has been offered to the nation in lieu of £2.9m in inheritance tax.

Dr Nicholas Cullinan, Director of the National Portrait Gallery, said: ‘The National Portrait Gallery is grateful to the executors of Lucian Freud’s estate and Arts Council England’s Acceptance in Lieu Scheme for this very important, extensive and generous gift to the nation. The Gallery has a strong association with Lucian Freud by virtue both of its permanent collection holdings and the highly successful 2012 Lucian Freud Portraits exhibition. This archive… will be a vital source of reference for anyone interested in the life and work of the artist or in portraiture in general.’

Culture Minister Ed Vaizey said: “This rare collection of Lucian Freud drawings and letters provides a fascinating glimpse into the work of one of our most pioneering artists. Bringing these never seen before treasures into public collections means that everyone can enjoy and see the early beginnings that shaped his most celebrated work."

Sir Peter Bazalgette, Chair of the Arts Council England said: “The Acceptance in Lieu scheme has been enriching our museums and galleries for over a century, as does this latest offer from Lucian Freud’s estate. This fascinating archive, which has never been exhibited before, offers us a real insight into the life of one of Britain's most compelling and influential artists.”