They're not fairly consistent, its a genuine misunderstanding of the system that they have to be. UK has a bit of nuclear, a lot of gas and biomass plant, some very useful pumped hydro and sizable interconnects to trade electricity with Europe. Everything is adjusted to match generation to demand. Generation is dynamic - Demand is dynamic. There is no panic when demand or generation changes, its handled.

There's a small amount of pre-existing pumped hydro storage in the system, but mostly it relies on the UK having already built a lot of CCGT plants which can cover the gaps.