Over 200 square metres of marble mosaics cover the interior walls of the north, south and west sides of St Andrew's Church. They were designed by the Victorian architect William Butterfield FSA (1814-1900). Believed to be based on mosaics he had seen in the Basilica at Ravenna, they were constructed by Italian craftsmen in 1884 and 1885.
Based on the notion that the Early English nave is a ‘twelve-apostle-arch’ construction, the two-tiered mosaics depict the twelve apostles, supported in the lower tier by medallions portraying the Patriarchs of Israel. The two tiers are divided by a band, which contains the text of the Apostles Creed. Each apostle figure is 1.8 metres high, and stands within a panel measuring 3.5 metres by 2.75 metres. The panels are decorated with fruiting palms and stars. Each apostle is identified not only by name, but also by those emblems traditionally associated with him.
The driving force behind the decoration of the church with mosaics was the Rev. Henry Bailey. DD who succeeded the Rev. John Wood Warter - the rector who had instigated a major restoration of the church in the mid 1800s. The Rev. Bailey's reasoning is explained in his booklet An Argument for the Decoration of Churches, which contains much information about the designs.