Shaun the Sheep-Seasons 3 & 4 DVD sets

I know Seasons 1 & 2 of Shaun the Sheep is available on DVD in the U.S. and the UK, but what I want to know is how many DVDs make up the 3rd and 4th seasons of Shaun the Sheep, because all I see are what appears to be single disc releases of the episodes in the UK.