You are not going to observe that in annual averages. As mentioned in my other comment, you can observe that very clearly in the energy production charts: https://gridwatch.co.uk/
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).