This locomotive is a `Princess Coronation` class Pacific (otherwise known as a `Duchess`).    The locomotive was designed and built at Crewe Works complete with the streamlined casing.  The streamlined casing was removed from those locomotives built with it in the late 1940s.
An example of this streamlining can be seen currently in the National Railway Museum at York. Stanier Pacific No.46229 `Duchess of Hamilton` can be seen in it`s original streamlined condition. This particular locomotive was based at Edge Hill Motive Power Depot at one time. It looks really quite magnificent - befitting of this class of locomotive as the most powerful to run in Britain.
The great engineer of the London Midland & Scottish Railway Company (LMSR) Sir William Arthur Stanier FRS,who designed this magnificent class of locomotive,was never too impressed with the use of streamlined casing as it made locomotive maintenance difficult.
The streamlining idea was championed by the LMSR Publicity Department rather than from Stanier`s Locomotive Department to compete with the London & North Eastern Railway (LNER).  Both of these two great railway companies competed against each other - and each had streamlined locomotive classes.In the case of the LNER it was the `A4` Class.