Per the article it’s not the top rate he plans to edit but the middle 40% rate which currently starts at £50,270. It’s a little more complex because there is also National Insurance to pay which drops when you hit the 40% tax rate so effectively you go from paying 32% total below £50,270 to 42% above £50,270 (for income above that level). There is a tax free band below £12,570 as well.
I’m simplifying because tax is complicated but roughly that’s how it works. As you move up tax bands you also lose amounts of other allowances like free dividend interest. Above £100k income it gets more complex because even more allowances are removed, especially the tax free band gets reduced.