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Lancelot took over as senior partner of trading house Dent & Co. headquartered in Canton, when his brother Thomas departed the company in 1831. He had a powerful hold over some agency houses buying opium from the Calcutta auction, including Carr, Tagore & Company, managed by Bengali merchant Dwarkanath Tagore.
Together with Thomas, Lancelot commissioned construction of Flass House, now a grade two listed building in the Palladian style, on land inherited from their sister in England's northern Lake District. The property would remain in the Dent family until 1972, when it was sold to banker, historian and writer Frank Welsh.
Lancelot and John Dent were consuls of Italy in Hong Kong.
Dent died in London on 28 November 1853 aged 54 and is buried in the churchyard at Crosby Ravensworth.