Boreray are from the island of Boreray which is just off St Kilda. Up until the 1930's the people living on St Kilda kept Soay (well kept is not quite the right word) - Soay lived on St Kilda) along with some more domesticated sheep on the island of St Kilda but they also had another flock of sheep on Boreray.
These were a Scottish Black Face and a Scottish Tan Face cross and were fairly feral as they lived on the island all year with just a visit from the St Kildean's every now and again (probably once a year to collect the wool)
When St Kilda was abandoned in the 1930's the islanders brought what sheep they could to the mainland but left the sheep on Boreray as impossible to catch.
In the 1990's a group of 7 sheep were brought off Boreray to try and preserve the breed and from that there are now just over 700 registered in Britain.
Sorry for the history lesson!!