https://atlaspragmatica.com/arguments-for-a-ubi-conclusion/
It seems to roughly involve the top 22% of earners having a tax bill that is up to 10% bigger than currently, while everyone in the bottom 78% of earners is unaffected or a net beneficiary.
35k makes net 12k (not taxed) + 18.4k (at 20% tax rate) = 30.4k net
In the conclusion, everyone gets a "UBI" of 666 per month, which basically doesn't even cover rent (https://www.statista.com/statistics/752203/average-cost-of-r...). If they would follow this German test, it would need to rise to 1100 pounds per month.
So in this scenario, that average full-time employee pays 48% flat tax on income:
35k taxed at 48% = 18.2k net, plus the 8k UBI leaves this average full-time employee at 26.2k. That is 4.2K less than before.
Looking at that graph at the end, I think there is some "creative graph-plotting" going on, unless I'm seriously mistaken in my calculation.
So how can this be the ideal calculation? The graph and conclusion seems to be in complete error. And even then, 8k per year barely seems like a 'basic income'.
There are plenty of places in the UK where the average rent is below £500 pcm, or even £400:
https://nolettinggo.co.uk/blog/10-cheapest-places-to-rent-in...
It's not a requirement of a UBI that every citizen should be able to live wherever they want, but it is an assumption that most citizens would have some income other than the UBI, or already own their own home, so it's not like everyone in the country would flock to places with the cheapest rent.
> Looking at that graph at the end, I think there is some "creative graph-plotting" going on, unless I'm seriously mistaken in my calculation.
Your calculations make sense to me, and I think it is reasonable to be distrusting of an economic analysis that doesn't provide the raw data for its most crucial graph (even as a link to a CSV file). The data in the article it links to is more complete, but approaching things from a different angle:
https://atlaspragmatica.com/arguments-for-a-ubi---the-realis...
https://atlaspragmatica.com/a-united-federal-britain/#commen...
Like you, they calculated the current take-home pay of this hypothetical person as £27,442 and, under the proposed UBI system, a take-home pay of £26,550. That's a one-off decrease of £892 which is about 2.5% of their gross salary.
For an imperfect comparison, Figure 5 here:
https://www.tuc.org.uk/research-analysis/reports/lessons-dec...
shows a similar real terms wage decrease in 2011, supposedly due to the political choice of austerity.
As another comparison, the Department for Work and Pensions estimated that 3.5% of their 2010-2011 budget was spent on administration:
https://www.whatdotheyknow.com/request/what_percentage_of_th...
Obviously replacing most benefits with a UBI won't remove all government administration costs, but it could lead to multiple society-improving outcomes (like improved health) which could reduce the over all tax level.