The Royal Memorial Chapel Sandhurst
The mosaic of Jesus Christ as we shall see Him when He returns, as described by the Apostle John in Revelation Chapter 1
The mosaic above the Lord's Table might be expected to be the work of a British or at least a military artist. The mosaicist was actually Count Boris von Anrep, a distinguished Russian of many interests, whose father's links to Czar Nicholas II led him to settle in England at the time of the Bolshevik Revolution. Some of his most well known works are the entrance floors of the National Gallery in Trafalgar Square, and also Westminster Cathedral, the private halls of The Bank of England, as well as many private commissions for notables of the time. Further information about the Count may be found at http://www.rkb-law.com/RR/insights/anrep/1boris.htm and http://www.nationalgallery.org.uk/about/history/building/1928.htm
A brief history of religious mosaic construction can be found at http://www.westminstercathedral.org.uk/art/art_mosaics.html which describes the mosaics of Westminster Cathedral.
Further information on Boris von Anrep may be found by clicking here

This symbol is not really a symbol at all but a monogram. It is the oldest known monogram of Jesus Christ. It is sometimes known as a "Christogram". The Chi and the Rho are the first three letters of Christ (cristos). The chi (c) = ch and the Rho (r) = r. This mosaic forms the centre-piece of the floor design in the oldest part of the Chapel - what is now the South Africa side chapel. It is not known who fabricated this flooring in what is a sometimes overlooked part of the building.