The historian George Herbert Guttridge (1898-1969) collected letters by 18th-century English and Scottish figures, primarily Whig politicians. He seems to have obtained these letters in groups of varying sizes, often from bookdealers. Spencer Research Library acquired the collection through the California bookdealer, Joseph Rubinstein, following Guttridge's death in 1969. During processing, the Guttridge Collection manuscripts were subdivided following their original provenance into the Correspondence of Sir William Lee; the Papers of David Erskine, 11th earl of Buchan; the Correspondence of Lady Mary Holland; and Miscellaneous Correspondence. A group of 154 printed pamphlets acquired at the same time have been cataloged separately as printed works.

This part of the Guttridge collection appears to have been obtained from Bernard Halliday's catalogue no. 242 lot 363 (Jan 1940) "Lee (Sir Wm., of Hartwell, Bucks) A Collection of Letters addressed to him... about 100 letters in all [QQ.171]." (Catalogue leaf found with G. acq. in Manuscript Records.) All the family names in the Conspectus (except for Greenhill, the Lees as writers, and the "Solicitor-General") are mentioned (although identities and counts are not exact); also mentioned are "and others", and the Wharton letter (now removed to MS 203B:16, since it is not obviously relevant to the Lee family). See MS 203B for other letters owned by Guttridge which might also have been part of this Halliday offer.

It is probable that the source of Halliday's material was the March 8, 1939 sale by Sotheby of "The Hartwell Papers" (the archives removed from Hartwell House). Lot 640 was "Chesterfield (Fifth Earl of) 6 Holograph letters, signed to Sir William Lee…Stanhope (William) 11 Holograph letters, signed…Stanhope (Eugenia)... July 17, 1773 -- Grenville (George) 16 Holograph letters, signed...; and others. (99 items)"

Later additions to the Correspondence of Sir William Lee in June 1989 were sections Ac-Ae (9 letters) found as a group in thr Phillipps collections.