Excluding the people who don't have enough and those who have so much that they'll always have spare money, for the middle majority, it's how you manage your money, not how much you have, that determines how much you save.
For example, how much is your mobile phone each month? Do you get a new high end phone every 2 years on a £50+ pm contract, or do you have a mid range phone, changed every 4 years, that probably averages out at less than half that?
If you had £50 left the day before pay day, would you spend or save it?
If you want something, do you save up for it, earning interest in the process and buy it when you see a special offer, or do you buy it when you decide you want it, whack it on a credit card so pay interest, as well as paying more for the item if it's full price?
Repeat decisions like that over time and the difference in what people can save could be hundreds of pounds a month, thousands of pounds a year, tens of thousands a decade.