A just published report commissioned by the UK's Department for Trade and Industry clearly shows that onshore windfarms are more than capable of commercially existing with lower subsidies than they do now. I'd go a bit further myself - some can exist quite easily without subsidies altogether.

Two forces are at play here;

1) The cost of wind turbines are still falling

2) The external cost of other energy sources - specifically coal and gas - are rising

It has been estimated that a 40% drop in the cost of windpower would make it the most competitive form of electricity generation. Some have predicted this happening by 2020. Far more likely is a 20% drop and a 20% rise in conventional fuels, yielding the same 40% drop.

Either way, as Britain's wind industry grows, there will be pressure to reduce subsidies, not increase them.