To actually answer OP's question, I spend £500 on rent, about £250-400 on living expenses, and a further £50-100 on various bills and direct debits. Of course, everyone's budget is individual so you can't use someone else as a guide. I'm guessing you're less interested in hearing about random people's budgets and more interested in figuring out how much money you need to survive.
First, work out your fixed costs. The main one is rent. This will be your largest single cost, and also the one thing that you can't easily cut back spending on, so it's really important to find affordable accommodation. If you're applying for university accommodation or are moving into a shared house, usually you will not be expected to pay any bills directly, so you only have to worry about that one big number.
After that, work out your other fixed costs. This will be personal to you, but could include mobile plan, Netflix, Spotify, gym subscription, etc etc. Add these costs to your rent, and you have a figure for your fixed overheads.
Everything else is disposable income, and you can be much more flexible about how you choose to spend this. You need to think about food, transport, toiletries, petty purchases (i.e study books, clothes) recreational spending (i.e alcohol, coffee, sports, cinema). For most people, I'd say £200 per month is probably the bare minimum you can get away with and still have a decent life. To feel comfortable, £300-400 would be better, allowing you to also have a bit of fun. Sure, there will always be someone claiming to live off £10 per week - and if you're happy to live off beans on toast, walk everywhere, and never leave the house then this can be done - but it's not realistic for most people. My advice is to always over budget, then you'll be pleasantly surprised when you have money left. That brings me on to the final thing.
Always save. You should ideally have at least £2,000 spare for a rainy day (if you feel like cheating, that can include your overdraft). Unexpected expenses can leave you destitute. Your landlord could evict you and steal your deposit! You might be fired from your part time job, or else find that you just can't continue working and also cope with uni work! Your dog might develop rabies and you have to pay the veterinary bills! (okay okay, that last one is unlikely). In fact they're all unlikely scenarios, but it's a good idea to have enough cash spare to manage any cash flow problems that might arise. This is particularly a problem for students, because we receive our maintenance termly whilst everywhere else works to a monthly calendar system.