Most of the current building dates from late Victorian times, when the estate came under the ownership of the Agar-Robartes family.
Henry Robartes, 3rd Earl of Radnor (c. 1695–1741), was succeeded as
Earl of Radnor by a cousin, but decided to separate the estate from the peerages by leaving it to a son of his sister Mary. By the late 18th century it had passed to Anna Maria Hunt (1771–1861) of Mayfair, London, the great-niece of the third Earl. In 1804 she married Charles Bagenal Agar, the youngest son of Irish peer
James Agar, 1st Viscount Clifden. The couple had three children, but by 1818 not only had her husband died, but also her eldest and youngest sons. Resultantly, over the next fifty years of widowhood, although mainly an absentee landlord – she preferred the social life of London – she was known to be a conscientious, benevolent, and charitable landlord and employer, who greatly improved the estate. On the death of his mother in 1822, her surviving middle son
Thomas Agar took up residence at Lanhydrock and adopted the Robartes name by royal warrant. Agar-Robartes was returned to Parliament for
Cornwall East in 1847, a seat he held until 1868. In 1869 the barony of Robartes held by his mother's ancestors was revived when he was raised to the peerage as Baron Robartes of Lanhydrock and of
Truro in the County of Cornwall. By 1872 Lord Robartes of Lanhydrock was listed among the top ten landowners in Cornwall, with estates of or 2.93% of Cornwall. Agar-Robartes had the east wing of the house demolished, leaving the U-shaped plan seen today. In 1880 he commissioned the architect
George Gilbert Scott to renovate Lanhydrock House. On 4 April 1881 a major fire destroyed the south wing and caused extensive damage to the central section. The fire started in the kitchen, and a near gale-force wind fanned the flames along the south wing and the ″communicating block″. New sections were built behind the south wing, including a kitchen block, in the style of the original building – which was unusual at the time. Agar-Robartes’s wife died five days after the fire of smoke inhalation, and he died twelve months later, reported to be of a broken heart. Their only son,
Thomas Charles Agar-Robartes, inherited the estate. Having been
called to the Bar in 1870, in 1880 Agar-Robartes was returned to Parliament as one of two representatives for Cornwall East. He appointed a local architect,
Richard Coad – who had worked as an assistant to George Gilbert Scott – to design and supervise the construction of a high-Victorian house from the previous adaptions of the
Jacobean house his father had planned. After renovations on the house were completed, Agar-Robartes moved his family there about 1885. Agar-Robartes entered the
House of Lords on the death of his father in 1882, and on 10 September 1899 succeeded his kinsman as
Viscount Clifden. In 1891, as chairman of the Agar-Robartes Bank, he took over the ownership of
Wimpole Hall, the largest house in Cambridgeshire. Moving his family home there, he later served as
Lord-Lieutenant of Cambridgeshire from 1906 to 1915. The Robartes family suffered great losses during the
First World War, including the heir
Thomas Agar-Robartes, who was killed during the
Battle of Loos in
France, while trying to rescue a colleague from no-man's land. As Agar-Robartes was unmarried, his younger brother
Francis later succeeded their father. In 1951 the house was designated a Grade I
listed building. ==Antiquities==