The Boulton-Paul Balliol stemmed from Air Ministry Specification T.7/45 which called for a 3-seat advanced trainer powered by a turboprop engine. Designed by John Dudley North, the first prototype flew on 30 May 1947 using, as an interim measure, a Bristol Mercury 30 radial engine and the second prototype, powered by an Armstrong-Siddeley Mamba turboprop, took to the air on 17 May 1948. The latter claimed the distinction of being the world’s first single-engine turboprop aircraft. Meanwhile, the Air Ministry re-thought its training requirements and issued Specification T.14/47 requiring a two seat advanced trainer powered by a Rolls-Royce Merlin piston engine to replace the North American Harvard.
The result, designated the Balliol T2, first flew on 10 July 1948 and soon thereafter an order was placed for a substantial number of aircraft. A few pre-production machines were delivered to the RAF’s Central Flying School in 1950, at which time the Air Ministry changed its mind again and decided instead to introduce a jet-powered advanced trainer, the de Havilland Vampire T.Mk11. Thus, the RAF College, Cranwell, and No 7 Flying Training School at RAF Cottesmore were the sole training units to be re-equipped with the Balliol until succeeded by the Vampire in 1956. The type also saw service from 1953 until 1957 as a target aircraft with No. 288 Squadron at RAF Middle Wallop
Meanwhile, a Sea Balliol T21 with folding wings and arrestor hook for deck landings was developed for the Royal Navy and saw service with No 781 Squadron at Lee-on-Solent and, until 1963, with No 1843 Squadron RNVR at Abbotsinch. Twelve aircraft were exported to Ceylon.
Four survivors remain of the 229 Balliols built. A Sea Balliol is on display at the RAF Museum, Cosford, and a T2 is maintained in display condition by the Royal Sri Lankan Air Force. Two other machines are in storage.