This mosaic image show a 6th century immigrant to Kent. He's the monk with the halo talking earnestly (through an interpreter) to the man with the crown on his head. The Benedictine monk is probably Roman and certainly sent from Rome. So he was an immigrant to the Kingdom of Kent. He is Augustine, who became the first Archbishop of Canterbury. The seated king is Aethelbert, the pagan King of Kent, also an immigrant - at least by descent from the invading Anglo-Saxons who drove the native Britains to the north and west. Sitting next to him and apparently praying is his Christian wife, herself an immigrant from France.
Augustine of Canterbury probably died on 26 May in 604 or 605 A.D. which is why the Church of England commemorates him today. Christianity had reached our shores several centuries before Augustine but that is another story.
Here's a life of Augustine of Canterbury told entirely in images from the stained glass windows of St Augustine's Church, Wembley Park, London. I especially like the sailing ship image at about 1.28 minutes into the video. If you want to understand the pictures you could look here or here.
Image Credit: Lawrence OP on Flickr, CC License