The markings F 57 on a No. 4 Mk 2 Enfield rifle indicate that the firearm underwent a Factory Thorough Repair (FTR) at the Fazakerley (Royal Ordnance Factory, Liverpool) facility in 1957. 
While original production of the No. 4 Mk 2 typically ended around 1955, these "F 57" marked rifles were earlier models—often No. 4 Mk 1 or Mk 1* variants—refurbished and upgraded to the Mk 2 standard long after the initial production runs.
Key Components of the Marking
F: Identifies the Fazakerley factory in England, which was the only plant to manufacture the No. 4 Mk 2 and perform these specific post-war upgrades.
57: Represents the year of the refurbishment, 1957.
FTR: Stands for Factory Thorough Repair, a complete overhaul where the rifle was stripped, inspected, and often fitted with new parts like barrels or stocks
Stock Markings: WS
The "WS" on the stock is a manufacturer's code for the wood furniture:
WS: This stands for W.S. Electronics Ltd., a contractor that supplied wood components (often the fore-end or buttstock) for Lee-Enfield rifles during and after WWII.
24 on stock is RACK no# for assigned soldier
The No. 4 Mk 2 Configuration 
The defining feature of a No. 4 Mk 2 (or a Mk 1/2 or 1/3 upgrade) is the receiver-hung trigger. In earlier Mark 1 models, the trigger was pinned to the trigger guard, which could cause consistency issues as the wooden stock swelled or shrunk. The Mk 2 design moved the trigger pivot directly to a bracket on the receiver, resulting in a more stable and crisp trigger pull.
Description
Manufacturer: Lee Enfield
Model: No4 Mk2
Action: Bolt 
Calibre: 303Brit
Barrel Length: 25″
Year: 1957
Features: Fazakerly Manufactured 
Comes with Spike Bayonet