It depends on a variety of different things:
- your social habits
- your financial situation
- your course
- your relationships
If you're a very social person, outside London I'd say try halls for a year, but in London...you might actually find that many of your friends are travelling back from nights out late as well, and having a 40-minute tube journey might not be attractive, but other people may be contending with 20-30 minutes from nights out anyway. It also depends how you socialise - if you like clubbing and parties, you might miss out on those, but only if you let yourself miss out. You won't not be invited just because you live at home, so make the most of the invitations, see if you can crash on someone's floor, and you should still have a lot to do!
London is obviously super-expensive. Yes, you'll get less funding if you live at home, but is £4k and only paying for transport (maybe contributing to bills/food, idk how you'd work it out with your family) better than £7k for everything, where £6k is already wiped out for accommodation? Do you have a job at the moment, and could you still do it if you moved for Uni?
How much contact time will you have? If you're on campus twice a week for a couple of hours, it might not be worthwhile living there, but if you're in 9-5 every day, the commute would feel worse (but then again, you might have a commute anyway, even in first year in Halls). How much of your course will be asssessed by group work? This is something I've found a bit difficult this year, when I'm living at home (1 hour+ away) and I only have group work set once a month or so. It's much more difficult to co-ordinate group work if you live away. But then again, the University has to accommodate mature students with families and other repsonsibilities, and can't expect people to instantly be free all week long to do group work...it just might take a bit of negotiating!
Do you have close friends at home that you would still see? Is there a partner who would be staying local, who you want to be near? I have 2 friends also commuting (to other Unis) living locally, and it's great for us, because we can meet regularly, and I don't just have my Uni friends, but them too. If I just had my family around here, I think I'd feel very different about living at home. My boyfriend lives 3 hours away though, and he'd be closer if I lived at Uni this year. But I'd have less time to see him, because I'd have to work more hours to fund my accommodation!
It's a really difficult decision to make, but it was 100% right for me to live at home this year. I'd already done a year in halls, one in a student house, and one in a solo appartment on a year abroad. At home, you already live with those people and know their habits, however annoying they might be. In halls or a shared house, you could get the loveliest, cleanest people ever, or you could get absolute idiots, and trust me, living with the latter group can be hell! If you can afford it, maybe go for it, and you can always change your mind for later years (or even that year, if your folks are cool!), but for the distance you'd have to travel, I can't see it having a huge impact, further than, "Oh you live at home...are your parents really protective or something?" type questions, which tbh are only asked by rich or judgemental kids (the first group are fine, but a little innocent, I guess).