The new Labor government didn't make a commitment to any specific numbers yet, but the 2021 Net Zero Strategy committed to reducing power generation emissions from 43.3 millions of tons of CO2 emissions to 16.6 in 2030.

For the moment let's assume the demand is constant (which it has been for the past 5 years) and that fossil fuel power plants are equally carbon-intensive in 2030 as they are in 2020. Then combining the numbers from the Net Zero Strategy and https://grid.iamkate.com/ gives 4GW of fossil fuel electricity production in 2030, which amounts to 13%, way above the 5% threshold.

On the other hand, right now UK is way ahead of that plan. It only called for a 13% reduction in emissions from 2020 to 2024, but fossil fuel power generation has actually dropped by 28.5% in that period.

To clarify, it has to be above 5% on average over the course of 2030 for this to resolve "YES", right?

The website from the description, https://grid.iamkate.com/, shows the live makeup of the power generation by default. But you can see aggregate data over the course of a year in the "all time" tab.

For example, right now the share of fossil fuels in the grid is only 10% in the live view, but averaged over 2024 to date it is 27%.

Also, I assume we are ignoring interconnects and counting them as non-fossil-fuel sources? Otherwise resolving this could be tricky, because the iamkate website does not provide sufficiently detailed information.