Virtually none of the gas power in the UK is traditional "peakers" aka Open Cycle Gas Turbines. There's a lot of Combined Cycle Gas Turbines. Gas is much more expensive in the UK than, say, the US and so it doesn't make much sense to build OCGT because although they're cheap to build they are very inefficient so your bid prices will be really high.

The curtailed windfarms are in the north of Scotland. There is currently not enough transmission capacity to export electricity from there to the south of England where the demand is highest. New transmission lines are under construction, but they wont be ready until 2029.