At a later point, probably during the English Civil War, the tower was deliberately damaged to prevent it being used for military purposes, and its uppermost storey was demolished.

St Leonard's Tower was constructed in the manor of West Malling, probably between 1077 and 1108, although its exact origins are unclear.

[2] This theory suggested that the tower was built by Gundulf, the Bishop of Rochester from 1077 onwards, who owned the manor and constructed Malling Abbey, a nearby nunnery.

[7][nb 1] At some point in the post-medieval period, the tower was deliberately damaged to put it beyond military use, a process called slighting.

[8] This probably occurred towards the end of the English Civil War, after the defeat of the Royalist forces in Kent at the Battle of Maidstone.

[9] There appears to have been an attempt to bring down the whole tower by damaging the stair turret at its base, possibly using gunpowder, which failed due to the spiral staircase's unusually strong design.

[11] The antiquarian Francis Grose noted in 1783 that the tower was then called the Old Jail, recording a local tradition that the abbey had used the basement as a dungeon, and the upper storeys as a prison for lesser offences.

[16][nb 2] By the 1930s, local magistrates expressed concern about the tower and the risk that it might fall over onto the grounds of a neighbouring private asylum, the Kent Sanatorium, endangering the patients.

[22] The square tower, or keep, is built of layers of local Kentish ragstone rubble and masonry, with white and grey tufa ashlar detailing and facing.