We've already had numerous periods where the UK's energy needs have been wholly met from renewables, there's actually a very good site where you can see all the stats from the National Grid in near real-time -
https://grid.iamkate.comIf you adjust the time range to all time (it has data for the last eleven or so years), where you can see the total demand dropping, and the renewables overtaking all of the other production sources.
To be clear, there is still a decent demand to supply gap, but it is dropping year over year, and given that we've gone from an average of 2.5GW/day to between 10 and 13GW/day in that timeframe, another 20 years or so and we should start meeting demand with renewables alone.
I'm hopeful that newer technology in that timeframe coupled with lower costs will encourage more and more generation growth from the sector, especially if more local generation and storage is encouraged, for example home solar/wind and home battery combinations. We'd also end up with a much more resilient power grid if most of the day to day needs can be met from local power systems, with the main grid only needing to supplement high stress periods and industrial and public communal requirements.