The major factor was reducing the use of gas which lowers gas prices. As a result the main beneficiaries weren't electricity users but gas users paying lower prices and saving 133 Billion.
We also have periods in the winter (so solar of little to no use), where we can have a week or two of no wind.
As the gas generators are not run constantly, they're more expensive than if they were. There are various (at least 3) UK "gridwatch" sites available, offering real time and historical generation mix. Maybe have a look.
From memory, so probably flawed, we still tend to depend upon nuclear and gas for around 40 - 50 % of our generation (nuke being low - say between 5 and 10).
Coal has gone from 32% to 0.
Gas has gone from 40% to 30%
How do you square these numbers with wind being responsible for the amount of gas burned?
A new wind turbine is built and plugged into the grid. Does this cause more gas to be burned or less?
[edit] and we might be talking at cross purpose here. I think most of the new capacity built now is to expand the production, rather than to reduce other forms of productions (in which case you might just keep around existing gas capacity if it was there, to your point).
It illustrates both the volatility of wind (which regularly goes to zero for at least a week), and how it is currently pretty much 100% offset with gas.