The collection charts the history of the 200-year-old practice from its establishment in the late 18th century until its closure and the death of the last managing partner in 2003.
Dickson, Archer & Thorp solicitors had a wide client base dealing with probate cases from families of relatively modest means to handling the business of many county families including that of the Duke of Northumberland.
Practice partners were also involved in governance both county-wide and more locally.
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The most recent acquisition was purchased following generous donations of £4,330 from the Friends of National Libraries and £1,500 from the now defunct Alnmouth Local History Society.
The additional items to be added to the collection comprise 124 lots including the first minute book of Alnmouth Turnpike Trust, 1752-1771; a fine plan of Charlton dated 1779 and papers relating to the building of Otterburn church, including some letters of John Dobson, architect, 1856-1857.
Coun Cath Homer, cabinet member for Culture, Arts, Leisure and Tourism at Northumberland County Council said: “This is a fantastic acquisition for Northumberland Archives. The records will provide an amazing resource for those studying local history. It will give an incredible insight into the history of Alnwick and vicinity.”
The Alnmouth Local History Group presented their donation to Northumberland Archives in memory of Fred and Gladys Bettess, who founded the society in 2002 but sadly passed away in 2013 and 1994.