Thanks! No problem at all. The final graph is loosely based on income data from this website:
https://www.gov.uk/government/statistics/income-tax-liabilities-by-income-range

Unfortunately, this dataset only provides income within a few set ranges, so to generate the graph I needed to apply some assumptions to get a dataset by percentile. The first assumption is that incomes vary smoothly (i.e. there are no sudden step changes), while the second assumption is that the remaining adult population that doesn’t show up in this table (23.2 million people) earn somewhere between £0 and £11,850 (amounts that are low enough to not pay income tax, and therefore not show up in the government’s income tax statistics).

Given these assumptions, it is possible to create a power-law line of best fit that gives very similar results to the government’s dataset. The formula I used for this line is y=x/((P-x)^(4/9)) where P is the total adult population of the UK, x is the total number of people earning below a particular income of the population and y is personal income. As an example, from the dataset, the number of people earning below £20,000 should be 23.2m + 4.1m + 6.2m = 33.5m, and using this formula we get 20,000 = 34.7m/((54.2m-34.7m)^(4/9)). Not perfect, but as a line of best fit goes, sufficient for a graph.

It is important to note that this graph does not account for any income from government benefits that people might receive under the current system – this is too dependent on individual circumstances to be able to include on a graph by percentile (https://atlaspragmatica.com/comments-on-ubi-posts/#graphing-existing-benefits). Many people on the left hand side of the graph would be eligible for benefits, but they are not calculated based on income alone – what people receive ranges from the situation of many homeless people who earn nothing yet receive no benefits, to the situation of the “working poor” renting in London who might earn £20,000 p.a. and be eligible for an additional £10,000 in housing benefit. At the end of the day, the latter group are likely to lose out somewhat under a UBI, but I would argue that subsidising rent in an expensive area is far less of a good use of government funds than helping someone to get off the streets (https://atlaspragmatica.com/comments-on-ubi-posts/#some-benefits-claimants-losing-out).

Regarding your second question – I can provide an example for how the proposed policy would affect someone earning £35k p.a.:

In the 2020/21 tax year, a gross income of £35,000 would result in paying Income Tax of £4,498 and National Insurance of £3,060 leaving a net take-home income of £27,442.

Under the proposed UBI and tax code, this gross income would be taxed at 47%, resulting in Income Tax of £16,450 but the UBI of £8,000 would also be received giving a net take home income of £26,550.