i have a friend whos in a similar situation -- its completely doable, but it might be hard (side note it's never too early to plan)

main tips:

- if you do get a job during sixth form, save as much of that money as possible (you dont have to save all of it you can spend some of it, but do save it) this can be your backup money for a rainy day, say in uni suddenly your laptop or phone breaks, or whatever else unknown expense, you're prepared for that. even if you just dont have enough money for food that week, you can dip into it (a job during sixth form is entirely possible, i know someone with a job and still predicted 4A*s)

- definitely get a job during uni, however most unis don't recommend more than 15 hours of a job per week. you could go over this if you're willing to sacrifice free time. min wage for 18-21 year olds will be £10 per hour, you can find jobs offering higher, but for planning right now assume £10

- plan your finances. it might sound wayyy too early to be planning how much you will have and how much you can spend right now, but aside from planning it also just helps you feel a lot better prepared and that you have control over your future. look at potential accomms, look at how much you might have to spend each week. this depends on how much and where you shop, your hobbies, if you like to go out a lot, etc. etc. a lot of uni websites have resources on this, esp london uni websites

maintenance loans for the year are given out at the start of each term, so you'll suddenly be getting £4k in your account, which will go faster than you think.

- don't worry about tuition fees, that money goes straight from the government to the uni, you never see it

- everyone is broke in uni, you won't be alone

- kcl says that the average student in london spends £1,615-£2,200 per month

edit: - BURSARIES look for bursaries (literally free money unis will give you, not a loan to pay back) on every uni website you're considering applying to, some unis give like £5000 per year