Charles Botolph, 24th Baron Mowbray, 25th Baron Segrave and 21st Baron Stourton
Alfred Joseph, Baron Mowbray, Segrave and Stourton died at Paris in April 1893, age 64, and his eldest son, Charles Botolph, 24th Baron Mowbray, 25th Baron Segrave and 21st Baron Stourton became the owner and occupier of the house and estate. Through his Baron Mowbray heritage, he was directly descended from a brother of Geoffrey de Mowbray, Bishop of Coutances, who was an adviser to William the Conqueror. Another relative, William de Mowbray, was one of the barons who forced King John to put his seal to the Magna Carta in 1215 and Charles Edward, 26th Baron Mowbray as a direct descendant, travelled to Washington, D.C. in 1976 with a parliamentary delegation that presented one of the four copies of the Magna Carta held by the British Museum to the U.S. Congress.
William Marmaduke, 25th Baron Mowbray. 26th Baron Segrave and 22nd Baron Stourton
The last Lord Mowbray, Segrave & Stourton to live in the house was William Marmaduke, 25th Baron Mowbray, 26th Baron Segrave and 22nd Baron Stourton, who resided there until his death on 7th May 1965 (except during World War II when he temporarily lived in Allerton House on the estate (built 1847/48 for the Steward) while the RCAF used the castle, nicknamed Castle Dismal, as their headquarters).
On 24, 25 & 26 November of 1965 there was a three day sale during which most of the contents of the house were sold.
No. 6 Group, Royal Canadian Air Force
In late 1942, Allerton Castle was requisitioned by the Air Ministry from Lord Mowbray, and transformed into offices and was the administration and operations headquarters of the Canadian No. 6 Group Bomber Command. On 6 December, 1943 their headquarters was moved from the temporary site at Linton on Ouse to Allerton Park and on 1 January 1943 reached operational status, no longer taking orders from No. 4 Group and reported directly to bomber command headquarters in High Wycombe. All 6 Group airfields were located in North Yorkshire. No. 6 Group was responsible for flight operations but also for accommodation and feeding of all personnel and the maintenance of aircraft.
No. 6 Group administration, operations and control was housed within the castle but a complete support airforce base was established on the grounds around Allerton Castle which consisted primarily of Nissan Huts providing accommodation, meals, recreation and all other facilities for the military personnel.