29% of working age uk households receive some sort of benefits. 20% of the population live in social housing, again lower rent.
As for those who don't live in social housing or receive benefits, something like 60% of first time buyers (much higher in London) receive money from parents or family members, these gifts early in life help to reduce the mortgage interest said couple would pay and allow them to borrow more or build more equity, putting them in a better position to upsize. This doesn't even take into account people like me and dh who got years of rent free living with parents, this is especially common for the children of ethnic minorities who will save up tens of thousands.
Free healthcare- this is a big one, it also frees up more leeway to save in early years. My MIL would probably have been bankrupted ten times over in the usa as a low income freelancer, my dh has 15 pages at least of medical records detailing all his various ailments including childhood epilepsy etc, his sister ended up in icu for 1 week, another sister has crohns, aspergers, adhd etc etc , she has never earned over 18k in her entire life but now she sits pretty in her house worth 650k and is mortgage free (did have some family help but mortgage paid from her salary)...she probably earns around 15k today and she has free public transport due to freedom pass and gets by though she has no pension, she even manages to go on uk holidays.
Only 7% of uk children go to private school and a lot of it is also paid by grandparents.
In summary:
Poor and vulnerable (single mums, disabled, low income <30k with families)- funded by state, social housing, nhs, will give minimum standard of living.
Middle income (35k outside London, 70k to 120k in London) - often gets help with deposit whether through rent free living or gifts, nhs; more likely to be dual income, those who don't will rent, space out children to afford childcare/move near parents for them to help with childcare
Higher earners- pay bulk of the tax, what they can afford will depend on where they live and their expectations..
But what you require has as much to do with the help you get and your circumstances earlier in life than your actual earnings. A civil servant on 35k who married a 56 year old guy who paid off his flat years ago and who lives in a 750k house she bought only 2 years ago is not wrong when she says that 100k is a very high income to live on though it may sound strange cos the person on the 100k income couldn't buy her a house..
in addition people on lower earnings would also have lower expectations than you re the kind of home they should get even with their luckier circumstances, I know a guy who is a graduate and his parents gifted him 300k to buy a home, he chose to buy a derelict 1 bed house in zone 4 and he told me he doesn't pay income tax (earns too little as a gardener) and has also never paid stamp duty, mortgage or rent. 300k may be a terrible budget in london but at the same time it would be unwise for someone with such unstable earnings to buy any bigger, he also went for freehold 1 bed so he wouldn't need to pay service charges. He is perfectly happy with his lifestyle.
Honestly though with the way things are, I don't think I could blame him as even if he did try to earn more I don't think he would achieve a substantially better lifestyle esp as a single guy and perhaps his parents may have given him less help.