There's been a significant rise in the amount of milk produced by larger dairy farms. In 2004/05 the bigger producers accounted for 48% of GB production but in 2007/08 this rose to 57%.

http://www.fwi.co.uk/Articles/2008/12/30/113659/57-of-gb-milk-production-controlled-by-fewer-than-4000-farmers.html

 That pretty much reflect farming in general. Those farms on the frontier of efficiency are moving away from those who are not. Think of it like this: the most efficient farms are improving their productivity at warp speed while the rest are plodding along at sub-sonic speed ...