Thanks for that. I thought a tine harrow would aerate and pull thatch out, unless I've misunderstood what they do.
The flail gives a fairly good finish, we're not a typical camp site, each pitch get's it's own field and the grass is paddock rather than a lawn.
We don't rake the grass up, that would be about 8 acres to do, so it's mown weekly and the flail mulches it reasonably well.
When you say raking, do you mean by hand because the area would be much too big for that.
If the harrow I linked to won't aerate and dethatch, what should I be looking at instead do you think?