Love - I do, actually - BIL in his early 20s coming out of years of stoner turmoil and teenage haplessness, now on his own and asked us to go over his budget for ideas recently.
Single man, no kids, min wage job, £1000 or so /month after taxes, pension and NI, rents a double room for £460/month all bills included in a shared flat near a train station which is on the high side (if he had a single room it would be more like £400-420/month but he wanted a bit more space). Had to hand over deposit and first months' rent, we were prepared to be guarantors but they didn't need it.
£30/month phone, £180 monthly train ticket, £50/week on food and toiletries (which could be lower but he eats a tonne as his job is manual labour), £80 for spends or save, a direct debit of £50/month into savings for a rainy day. It's very tight, he knows where every single penny is going.
And indeed, he has discovered it's not that much fun to worry all the time on such a strict budget or to sit in his room all evening avoiding his flatmates or not seeing friends because he can't stand his round without a huge hit to the budget so he's been picking up evening work, asking for more hours at his day job, and working on getting more qualifications at night or on the weekends so he can get a better wage.
Again, this is for someone able bodied, fit to work, no kids or caring responsibilities. The moment pets, disabilities, children, maintenance payments, saving for a deposit etc materialise, then of course it's a different story.