The Collection, originating as it does from a solicitor's office, contains what are in the broadest sense legal records, although it includes many types of document lying beyond this legal definition and pointing to a custodial role by the solicitor of some of the family's more general papers. The interest of the core archive lies for the historian particularly in a breadth of subject matter, which includes: urban estates, rural estates, the exploitation of minerals, port and railway developments, famously bizarre law suits, and the amassing of great wealth and great debt.
In date the coverage is strongest for the period from the Restoration to 1927 (and the formation of the Welbeck Estates Company Limited), although some earlier deeds do exist, particularly for Northumberland from the 16th and early 17th centuries. Rentals, estate accounts and incidental records are richest for the later 18th and very early 19th centuries. This was the period of the 3rd Duke of Portland (1738-1809), whose correspondence and financial difficulties generated a major part of the Collection. The later 19th- and 20th-century material details the buying and, increasingly, selling of small properties, and the development of coal mining and those towns and villages dependent upon it. All of the family's estates, and the mechanisms of their acquisition and disposal, are recorded in some form.
Some estate papers of Edward Harley (1689-1741), 2nd Duke of Oxford and Mortimer, are also found in the Collection. These papers were inherited by the Dukes of Portland following the marriage of William Bentinck (1709-1762), 2nd Duke of Portland to Lady Margaret Cavendish Harley (1715-1785), daughter of Edward. They complement other Harley Family Papers found in the Portland Collection (Reference: Pw 2 Hy).
Litigation is dominated by triangular disputes between the 6th Duke of Portland, the Butterly Company and the New Hucknall Colliery Company in the 1900s. There is also comprehensive coverage of the curious Druce case (1896-1913), which concerned a claim to the ducal title, based on the alleged double life of the 5th Duke of Portland as a London merchant.
The management of urban property is represented by the contrasting development of 18th-century Marylebone, London, late 19th-century Hove, Sussex, and Ashington, Northumberland. Alongside these are the urban estate of Soho, London (1730s-1800s), and the development of Troon, Ayrshire as a coal port. The agricultural heartland of the Portland estates, in Nottinghamshire and Derbyshire, was transformed in the nineteenth century when coal mining led to the creation of colliery villages such as Creswell and the expansion of existing places such as Bolsover and Mansfield.
A cycle of wealth and debt is evident from the papers, which provide more evidence about the downward turn of the eighteenth century (notably the 1st Duke's disastrous speculation in the South Sea Bubble, and the 2nd Duke's indulgence of his passion for book collecting) than about the rapid revival of fortune in the nineteenth.
Of considerable significance is the correspondence series, much of which comprises political and official correspondence of the 3rd Duke of Portland, closely related to his papers in the Portland Welbeck Collection (Pw). This was clearly distinct in its creation from the bulk of the solicitor's papers, and forms a separate sub-group of the archive. For further description see Pl C.
Finally there are papers relating to the Heaton/Heaton Ellis family (managers of the Dukes of Portland's affairs before Baileys), including business undertaken on behalf of other clients. Some items are present which seem to concern clients of Baileys, Shaw and Gillett, not in any obvious way related to the Portlands, Heatons or Baileys. There are also some documents relating to the operations of Baileys as a firm.