Patrick Robin Gilbert Vanden-Bempde-Johnstone, 4th Baron Derwent, (26 October 1901 – 2 January 1986), was a British peer and Conservative politician.
Derwent was the younger son of Hon. Edward Henry Vanden-Bempde-Johnstone, younger son of Harcourt Vanden-Bempde-Johnstone, 1st Baron Derwent. His mother was Evelyn Mary Agar-Ellis. He was educated at Sandroyd School then Charterhouse School. He succeeded as fourth Baron Derwent on the death of his elder brother, George Harcourt Vanden-Bampde-Johnstone, 3rd Baron Derwent, in 1949 and took his seat in the House of Lords. In September 1962, Derwent was appointed Minister of State for Trade in the Conservative government of Harold Macmillan, and when Alec Douglas-Home became Prime Minister in October 1963 he was promoted to Minister of State for Home Affairs. He retained this post until the Conservative loss in the 1964 general election. He never held ministerial office again but served for many years as a Deputy Speaker in the House of Lords.
Lord Derwent married Marie-Louise Henriette Picard, daughter of Albert Picard of Paris, France, in 1929. He died on 2 January 1986, aged 84, and was succeeded in the barony by his son Robin Evelyn Leo Vanden-Bempde-Johnstone.