Golly. I don't think I've ever heard someone suggest one universal, fixed rate of tax in my life! Not even Farage is suggesting such a thing.
Just doing very rough calculations, that would suggest that everyone of working age (18-65), given today's governmental spending, would pay £24,000 in tax. Currently average gross annual earnings are £37,000 for full time employees and £13,000 for part time.
Obviously, governmental spending would have to be slashed to the bone and there would be people dying on the streets, homeless, unfed and sick. Crime rates would shoot up because of the need and because there wouldn't be enough funds to run a police force. My guess is that civil unrest would quickly follow, and those that could would leave the country, cursing the poor for ruining the country.
Yup, that would be fair.
And, of course, sensible. In fact, even the very wealthy owe their standard of living and their comfort to the existence of a functional, stable economy society. We saw during covid, the importance of delivery drivers, supermarket workers, bin-men etc the low paid who don't earn as much as you want them to pay in tax.
There are many different ways of calculating 'fairness'. You suggest a single flat sum. Others might suggest a single percentage (there are few people on here who, when talking about finances in a marriage suggest splitting costs equally, when one person is earning lots and the other is a SAHM or on a significantly lower wage). The political consensus across all parties for generations has been a progressive tax system; so you're quite the outlier.
You say you feel despised. You're probably right