The collection had incurred two major misfortunes before its transfer to Cambridge. During the war, the bulk of the Thurso papers that were being stored in Liberal Party headquarters in London were destroyed by an incendiary bomb. After the war, a large portion of the remaining papers were destroyed in a fire that broke out at Thurso East Mains where they were being kept in a room above the laundry. Most of the papers that were rescued from this second blaze were severely damaged both by the flames and by water from the firemen's hoses. Section VI of the collection contains the charred remains of this accident which are too fragile to handle whilst those damaged files which have already been repaired by the Conservator have been placed in their appropriate places within the collection.

In Viscount Thurso's own lifetime, he was asked by the Scottish Record Office (in 1966) if he would deposit there the papers relating to his tenure of the office of Secretary of State and these papers were consequently deposited in Edinburgh early in 1972. At the same time, Viscount Thurso's son began the transfer of the residue of his late father's papers (the 1st Viscount had died in June 1970) to Churchill College. These papers are our Sections I and II.

In January 1973 the Scottish Record Office agreed to transfer their Thurso papers, relating to his time as Secretary of State for Scotland, to Churchill College, having first xeroxed them. This collection was catalogued in the National Register of Archives (Scotland) Survey 189 (Additional) and comprises Section V of our Thurso collection.

By the spring of 1973, Viscount Thurso's secretary, Miss Cynthia Metcalf, was sorting and listing the papers that were to be deposited here in May and September that year as Sections III and IV. As Section VIII (the family correspondence and business papers) came in much later than the rest of the archive (in 2010) and consisted of different material to anything else in the archive, it was given its own section rather than add it to any existing series.

Within each series, the papers were numbered by box, so instead of the normal running file numbers, the papers are numbered by files within individual numbered boxes.