It concluded that there is literally not enough renewable energy potential in Great Britain (e.g., cover every square millimeter of space with solar panels) to do so at then-current energy consumption rates. It also pointed out problems with approaches like "giant solar fields in the Sahara" (the requisite solar fields are, well, roughly the size of Germany in terms of required area). Nuclear is technically not a renewable energy resource, but it does have requisite power generation capabilities--and very staunch anti-nuclear activism that makes expanding nuclear difficult.
All in all, quite an eye-opening read.
That is false, though. Just a little math shows why.
The UK is 242,500 km². Nameplate solar capacity on that would be on the order of 150MW/km², so 36 Terawatts. UK average electrical consumption is 32 /Giga/watts. Assume solar produces 1/4 of that 36TW on average when it's sunny during equinox, so 9TW. Even on a pretty cloudy day on the winter solstace in London, you're still going to produce at least 1/10th to 1/20th of that much, so worst case of worst cases (cloudy day on solstice) you're looking at 450GW average if you cover the entire UK in solar panels. That's still over ten times the UK's average electrical consumption.
(I used UK instead of Great Britain, but that doesn't make much difference.)
I mean, the overall point that you wouldn't want to power the UK on solar alone is totally and completely valid (and I fully support the Hinkley Point C nuclear power plant, by the way), but the idea that it's literally not possible is BS.
It's an absurd claim to say it's impossible, and there's almost nothing more annoying than a source claiming to be "without the hot air" actually being full of plenty of hot air on absolutist claims like this. You don't correct BS by using equal and opposite BS.
(Most energy advocates I know do this... both renewable advocates and nuclear advocates, exchanging BS about the opposite technology. It's a clean energy circular firing squad, with the climate in the middle.)
The total chart at the end came out to <https://www.withouthotair.com/c18/page_103.shtml>, with solar making up about 68 kWh/d per person.