The first domestic sheep were introduced to Britain during the Neolithic c. 4000 BC. The only evidence of these sheep comes from their skeletal remains and they are presumed to have a coat not dissimilar to their wild forebears with bristly fibres, known as kemps, obscuring an undercoat of fine wool.
It is thought that the small, brown Soay sheep that survives in a feral state on St Kilda off north-west Scotland best represents Bronze Age breeds in Europe, evidence for this coming from the similarity of skeletal remains with those of the Soay, and the similarity of wool in Bronze Age cloth with the fleece of the Soay. This wool was already much less hairy than the coat of wild sheep.
Further changes to the coat appeared in the Iron Age when white sheep seem to make their first appearance. White wool has been found in a Scythian burial mound in central Asia dated to c. 400 BC. But there was in fact a range of colour: black, white and grey, in addition to the brown of the Soay. Evidence for this comes from textile remains and surviving breeds.
Roman textiles from Britain and the Continent show that more changes in fleece type took place at that time. The predominant wool type at that time, in addition to being white, was fine to the naked eye. It is presumed that selective breeding was taking place at this time.
Sheep were found everywhere in England during Saxon times, as judged by place-name evidence. Saxon wools are comparable to those of the Roman period, ranging from hairy medium wools through the generalised medium type to the true medium fleece and even the fine fleece, evidence for the latter including some yielded from the Sutton Hoo burial. At around this time, many northern areas were occupied by those of Viking descent and it is possible that some northern breeds contain Norse and Danish influence.
In the early Middle Ages, the main function of sheep was to provide milk to make cheese for winter food; wool, manure and meat were by-products in that order of importance. Breeds in the modern sense did not exist, although a classification of sheep by fleece type was already in use by wool buyers. Records and the wool in cloth remains confim the persistence of coloured sheep. The predominant fleece type appears to be the hairy medium/generalised medium fleece comparable to the surviving short-tailed and vari-coloured breeds in Orkney and Shetland. Skeletal remains support this conclusion.
Reference: Ryder, ML. 1984. Medieval Sheep and Wool Types. The Agricultural History Review 32.1: 14-28