The LCBP surreptitiously removed grant funding for solar photovoltaics on 03/02/10 at 17.00 with only a few minutes notice.

The reasoning is simply that it was too good a deal, and they realised that. 

The returns are still much better than those that can be found anywhere else, be they ISAs or bank account with 7-8% tax free return still available - though obviously this depends on your roof.