Not exactly an expert but I'd say they were carp that could comfortably be caught using pole methods and would build a large net weight. Say 5 to 10lb'ers ?
Quite a few commercials favour carp in their lakes as they are quite hardy and resiliant to handling <duck> and can and often do promote the fishery when large weights are reported. Saying that 100lb of carp is a lot easier to catch than 100lb of Roach 
A couple of years ago the answer would probably have been 8oz-3lbs.
Now it's more likely to be 2lbs-5lbs.
As Dave has said a lot of these waters were created to enable anglers to do the "ton"........100lbs to the uninitiated.
However one thing that carp are very good at when faced with lots of anglers throwing plenty of bait at them is...... GROWING
On some of these waters it has got to the stage where you need less than 10 fish to do the ton.(Drayton springs to mind)
This has resulted in match anglers turning into "speci boys" and at waters like drayton it is more common to see carp rods and baitrunners than normal match tackle.
Personaly i can only see this trend increasing,as more and more commercials generate an increasing number of specimen carp (20lbs+) that are all but uncatchable on conventional match gear.