The data quoted in that chart is very old (from a 2011 report). It is not clear if it is referring to the deployment of new nuclear but I would say it is not based on the numbers. New nuclear is about 2-4 times the price of renewables (more for SMRs) and only heading in one direction. Also, renewables can be deployed in a fraction of the time it takes to get a nuclear plant up and running, and time is of the essence for the climate now. Anything being built now won't stand a chance in the market by the time it comes online.
Just on the windy/sunny thing (a meme in climate circles). Yes those that design and balance the grid do understand this variance. The UK will need peaker plants of one technology or another until enough renewables are deployed and storage catches up. And it will.
You might not be aware that nuclear plants are also shut down regularly for a variety of reasons. Half of France's nuclear power plants were offline for one reason or another in 22. They are not as reliable as often imagined, and can only be used as base load. And those plants built beside the sea or rivers (all of them ) will have their own problems as the climate changes, with sea level rise and droughts. There is also a different problem with cheap renewable power in the market compared to more expensive base-load nuclear power, the flip side of the coin, but that is a whole other discussion which I won't get into.
Anyway in short, existing nuclear I'm down with but new stuff doesn't make sense is where I land.
We can't rely on an assumption that storage will just catch up for a whole country though. Is there anything available that's currently proven on the scale of the UK that could store 5 days worth of power for 75% of our needs? I'm sure storage will improve in the future but until we're nearer that time we need consistent reliable power which nuclear provides. Yes of course it needs maintenance but France didn't experience energy price spikes to the same degree as other countries because of their large nuclear fleet, their fleet is also quite old now I believe.