The cost for balancing the grid is not increasing per unit of unreliable energy put in it. They have always been very high and always been there but so far, network operators on orders by those making policy found nifty ways to use safety margins in the grid plus accounting tricks to keep them from public view. If people would have caught on early on the true cost of all those green gadgetries, they would likely have objected. But in true step-by-step fashion, the frog was cooked slowly so it did not jump out of the kettle. That said, it might still jump.
Net balancing costs were £506m in 2015. The system pressures mentioned above have pushed the net cost in 2020 to £1.3Bn, 67% higher than 2019 (£794m).