If I remember rightly it's illegal to chuck any 16 year old (or younger) out and make the deliberately homeless (from a rental point of view). Make him approach the council social services and explain the situation. They must rehouse him, as it's illegal for anyone at the age of 16 or under to be homeless, the council must rehouse him.
He should contact the YMCA, or a charity called Street Link that deals with homeless teenagers.
Another good source is the Salvation Army, as they have some great resources for the homeless, they even do a missing children's help line.
Is his father on the scene, he might be able to help?
As for his mother, as it's been said before, she is still responsible for him, and as such cannot simply chuck him out, without another place for him to go. I'm not sure she still may well be getting child benefit for him until he has found a job. I know my parents were for me. That money is for him, and as such he should receive it, or it should be stopped if he is no longer living with her. It needs to go to the person who is buying clothes, food etc for him. He may even been given a guardian for his care and well being.
If he is still at school, he must tell the school the situation, as they may have resources that can help.
Unfortunately some parents do not know the law as regarding minors, but the law is behind the teenager, so he shouldn't worry. As for his mother she needs good kick up the pants, and yes I'm old enough to be the teenagers mother, and I would never under any circumstance chuck a child out on to the streets.