Hi, I see you're from the UK, so none of the statute of limitations stuff people are talking about applies. It's never too late to report abuse here. You don't need to speak to a lawyer either. Even if this was to go to court, you'd be a witness, so at no point would you need a lawyer.
I spoke to someone at rape crisis about it (by email) and they talked me through what would happen. Actually I didn't originally speak to them about that, but that's where the conversation ended up going. I'd recommend doing that. I was under 16 at the time so I imagine reporting as an adult would be different to reporting as a child. With kids there is a joint investigation between the police and social work, so I was interviewed by both of them (at the same time).
Okay, I googled. This isn't the best link but it tells you to call 101 and they can put you through to a specially trained officer. https://www.nspcc.org.uk/preventing-abuse/signs-symptoms-effects/non-recent-abuse/
I'm not sure if the police would arrest your abusers right away, but they'd definitely be asked to attend the police station to be interviewed. The only other thing I'd add is that once you report it's pretty much out of your hands. The whole thing becomes about the crown prosecution vs the abuser. You just become a witness. It's really kind of a strange feeling, like you're just some cog in their machine. Like it's no longer about justice for you, it's about results for them. I hope that doesn't sound off putting. It's just something that surprised me at the time. I suppose I had the image of fighting my abuser in court, but actually it's just their lawyer fighting the CPS lawyer while the abuser sits there saying nothing and you're not even there. It can also be a very long process, and even when nothing is happening with the case (which is a lot of the time) it's still stressful having it hanging over you. I still think it can be a worthwhile thing to do though.