
The original organ was built about the year 1750, either by the firm of Jordan or England, both famous organ builders of the early 18th century, and was erected in a gallery at the west end of the church. It was probably a two manual instrument, without pedals, and for that period, was a good one.
It remained as such in the gallery until 1850 (the period of Victorian restoration) when it was removed to the Lady Chapel, rebuilt and enlarged by Wm. Hedgeland of London, a third manual being added.
In 1895 further rebuilding and enlarging were carried out by Henry Willis, a master of his craft who designed and built organs in cathedrals from Truro to Aberdeen, as well as for the Royal Albert Hall and St Paul’s Cathedral. His work on the Westbury organ at this time included a new pneumatic action, new pedal board, and manuals. It is not known how much new pipework was added at this stage. In the dismantling of the organ in 1965, some details of the work carried out by Willis were found pencilled on a part of the timber frame, as follows: "This organ was made tubular by W. Stiles and R. Simpson and finished by A. Deeks, August, 1895".
In 1933 the organ was under the care of Griffin and Stroud of Bath, who installed electric blowing apparatus. Tuning and maintenance were subsequently taken over by Rushworth and Dreaper, who cleaned and overhauled it in 1948.
The last renovation took place in 1965 when the organ was moved from its position in the Lady Chapel and moved to its present location with the pipes at the west end of the church. Rebuilding was first considered in 1962, and the organ was dismantled in June 1965. Rebuilding was completed in time to rededicate the organ at the Midnight Mass of Christmas 1965.
The moving of the organ to the west end of the church involved some major alterations including the construction of a new gallery within the tower area cantilevered into the nave to hold the organ pipes. To accommodate the console in the choir, alterations to the chancel were necessary, which also gave the opportunity to change the layout of the choir stalls, make alterations to the floor levels, repave the floor and move clergy stalls into the choir from the nave. It also allowed the North chapel to be restored to its former use as the Lady Chapel.
The pipe front was designed by Leonard Hatch, organist of the church in 1965, in conjuction with Edward Fry, organ consultant, and Francis Hannam, architect to the church.