Have a look at "Gridwatch" - but not just once or twice.
Really study how the various supply sectors respond to the demands of the grid, depending on what's synchronised and how the weather is behaving. Watch how the sources interplay ...
FYI it takes several hours to "heat up" the boilers at a fossil fuel powered plant, or you are using up a lot of fuel to keep them 'nearly' ready to generate. Planning for what is needed [as in 'for the next five minutes' as well as 'for the next decade'] is the black art and has been royally mucked about by both privatisation / subsidy policies and largely ignoring climate / environmental factors ...
The UK's [and the world's] problem is that storing electricity, at the quantity required by the grid / consumers is very difficult.
In case anyone wants to know - FYI[2] - I used to work for a company that was in the relevant engineering field - ie power generation & distribution.