The lowest bracket - is that meant to be without housing costs? I am sure I've seen this sort of thing on here before - if you have no housing costs, i.e., you own your own freehold property, then I think the £1k a month or thereabouts is doable. That's where I hope to be in a few years time - I'll get my state pension and a small private pension of about £2,500 a year. However, that means I won't qualify for pension credits. And of course there's still all your utilities and council tax. Also if you are in a leasehold you might have quite high service charges and ground rent.
I saw a thread on here before Christmas that really made me cross; a retired/about to retire poster saying that after all outgoings her and her husband ONLY had £3k in cash each month and wondering if she'd be ok, would they manage on that ... (they owned 2 properties if I remember rightly). A couple of people (not many) said well of course you can afford to live on that, and then the poster was like "oh poor me, I was only asking" - that sort of attitude. I think to call it disingenuous is being polite!