I have a cousin who's baby mother won't let him see the baby and she lives in a environment were there is drug use and is not very clean. And she is not very stable finacally and mentally what should he do to get custody?

Something that really gets my back up so please do not take this in the wrong way but >>
He is worried about the babies safety
He is worried abot the environment baby lives in
He is worried enough to involve you
HE IS WORRIED FULL STOP!!

Why is he wasting time ? Why has he not involved the local authorities ? Does he not watch the news or read the papers ?

I am sorry but you should be on the phone right now talking to people who could help this baby !

Never mind fighting for custody he needs to fight to get someone in authority to go and check the safety of his baby and then he can go and speak to a solicitor and start proceedings for contact/custody which can take months and months !

You need to call Social Services, they will check in on the baby and ask the mother questions. From there, if they find that these alligations are true, they will take the baby from the home and most likely hand the baby over to the father until the court date.

I to agree with the people above if it is I'm the baby`s best welfare call the cops on the mother while she's using the drugs or you know that drugs are in the house. And if the mother is unstable that can't be good for the kid

You hire an attorney to file for temp custody and a custody hearing,
You document all of the issues by getting children servies involved and perhaps the police

Remember unless you can prove it , with evidence that is allowed in court, it is not happening