Hi, thank you for your question. Just a bit more information required to fully assist you:
-How old is your son?
-How many nights, on average, does he stay with the father?
-Does the father have any other children in his care, if so how many?
-Is £400 per week income a gross or net figure?
Thank you for confirming. So long as your 16 year old remains in education (ie. A-Levels) or approved training, the father has a responsibility to pay child maintenance to you - on the information you have provided the legal obligation is closer to £60 per week that he should be paying.
In relation to housing him, this will be your responsibility and if you are unable to suitably accomodate him and the father has the resources to house himself, and the child separately, then this can be pursued in a court application - but given his relatively modest income it is unlikely that he has such resources and his only legal obligation will be in relation to child maintenance.
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