Developed from the 44XX class introduced two years earlier, engines of the 45XX class were basically similar but with larger driving wheels for extra speed. Very successful in service, being capable of 60 miles per hour between stations, they were generally based towards the west of the system, where curves were sharper. From 4575 in 1927, they were fitted with larger, sloping-top tanks for increased range. A total of 175 were built.
Withdrawal of the class began in 1950, and they had all gone by the mid-sixties, as branch lines either closed or were taken over by the diesel multiple units.
As a member of the 4575 sub-class, 5572 was almost the last produced (two from the end). Based for more of its life in the South West, in its later years it moved to South Wales where, unusually for this class, it was equipped with auto-gear for working push-and-pull trains on the valley branch lines. Of the thirteen engines of this very useful class to have survived into preservation, 5572 is the only one so fitted.
Built at Swindon in February 1929, it was withdrawn by BR in April 1962, being sent to Woodham Bros of Barry for breaking up. It was bought by the Society in August 1971, and sent to its Taunton depot, being partially restored there before coming to Didcot in 1977. Having reached the end of its ten-year boiler certificate, it is awaiting heavy repairs. It has seen service on preserved railways away from Didcot.