Althorp Papers. Vol. mmdcxi. Letters to Lady Mary Elizabeth Ponsonby, wife of Sir Henry Ponsonby, mainly made up of family letters from Charles Robert and Margaret Spencer; 1890-1915, n.d. Sir Henry's grandmother was Henrietta, 3rd Countess Bessborough, daughter of John, 1st Earl Spencer.
Althorp Papers. Vols. mmdcxii, mmdcxiii. Letters from Sir Thomas Biddulph to Queen Victoria with additions in her hand. A few of the letters are addressed to Sir Thomas and passed on by him to the Queen; 1866-1878, n.d. Two volumes.
Althorp Papers. Vol. mmdcxv. 1. General correspondence of Sir Thomas Biddulph; 1856-1877. 2. Letters to Lady Mary Biddulph, wife of Sir Thomas; 1849-1892, n.d.