Where to get support for a burned out 8 year old?

Hello All,

I am brand new to the forums, so apologies for asking for something before contributing, but we need help.

I am the Dad to a beautiful, amazing, and currently struggling 8 year-old. Some changes in her school life (or it could be something else) have prompted a huge deterioration in her ability to function. 

She is alternately clingy, anxious, and furiously angry. The level of conflict with her brother has shot through the roof. Tics and stimming have increased. She seems in a state of constant overwhelm.

We are trying to support her as best we can, but right now it's not enough. It's just me, my wife, and the two kids. We have pretty much zero family support and zero support as yet from the outside. But we need something.

What would you advise? I worry that she is in crisis. I am worried for her. And I am worried for us. 

What kind of support has helped you in the past if any of you have experienced something similar?

We are based in Brighton.

Thanks in advance.