In 1649 during the Civil War following the Battle of Uxbridge, it was used by Cromwell's Parliamentary forces as a store and a barracks.

[4] During this time they damaged the chapel, took lead from the roof to make musket balls,[4] and created a new door in the east wall.

[1][4] In 1897 vestries were added, the windows were restored and the pews were rearranged in collegiate manner.

[1][4][5] During the 20th century the fabric of the chapel deteriorated, and in the winter of 1962–63 part of the roof fell in.

[4] Oxhey Chapel is constructed in knapped flint and red brick, arranged in alternating squares forming a chequerwork pattern.

At the east end is a four-light window, above which is a brick gable containing a plaque with the dates 1612 and 1963.

The west door is surrounded by a doorcase consisting of carved Corinthian pilasters and an entablature.

It has an octagonal base, a richly carved circular bowl, and a dome-shaped cover.

At the west end is a marble memorial tablet to John Askill Bucknall dated 1797 by C. Regnant.