"The present church is Norman in foundation, with the nave being the main surviving part from this era, and Roger du Pont L'Eveque, Archbishop of York from 1154 to 1181, is thought to have been the builder in about 1175 AD." This and more history and detail is at http://www.standrewschurchdown.org.uk/history.htm and full architectural details are at https://historicengland.org.uk/listing/the-list/list-entry/1305148

"At the end of the 19th century it was felt that the old church of St.Bartholomew's on Chosen Hill, inaccessible as it was in bad weather and difficulty of access for the elderly or infirm, could no longer adequately serve the needs of the parish's growing population." http://www.standrewschurchdown.org.uk/history.htm Hence St. Andrew's was built further down the hill.