Ways to ask/ tell my mum that i want to move in with my boyfriend?

So my mum is very protective of me and considering I'm the youngest of my siblings she is a lot more strict with me. So my boyfriend is moving into this apartment soon and I really want to move in with him, plus we are both getting a boxer dog and it seems more sense to move in with him instead of just lumbering him with a dog, plus as its a puppy it will need attention 24/7 and my boyfriend works from 4am till 2pm and 2pm til 12 am on alternating weeks and its a long time to leave a puppy alone. How can i say to my mum that i want to go? because i know her answer will be no. Plus are there any UK laws in place to say that my mum still is responsible for me as I am 17. Thanks guys :)