I need motocross help?

I need help getting into motocross, i used to bmx, skate, inline and dirt jump. All of these were fun but i want to try something more exciting and dangerous. I live in Stoke, UK. I will start when im 17 (which is not that long) and i was wondering, where do i go? and what cc bike should i have? and what bikes are good for racing and jumps?