curious, please give insight

this is probably something similar to what's been asked before, but not at the same time.   currently i am planning a trip to the uk to visit my boyfriend for a month, and i will be leaving my six year old son here with my mother.  if everything works out accordingly, we've discussed marriage and having myself and my son move over.  

problem is, i'm not sure what to do in regards to my son's father.  we were never married, and he is currently married with two other children.  we do not speak very often, and never really on good terms.  he doesn't exercise his visitation rights and it's not just because he lives in another state, he simply chooses not to.

so my question is:  how will this work?  i have sole custody, but i know he will not sign over his rights.  should i, simply, consult an attorney or can anyone give me a little insight as to how a situation like this is manageable?  i do not want to have my six year old travelling, constantly, back and forth between the uk and the states!  please help.  

In terms of legalities of moving your child and a visa:
If you have sole legal & physical custody and that is granted by a court order there's not much that the father can do besides go to court and fight for custody.

However, it is my understanding that if your court order includes visitation and the father chooses to exercise that right, then you will need to comply so your child will need to travel. You may want to consult a family law attorney and see if you can have the visitation removed.

If you do have a court order then if you do chose to move to the UK the visa process is very simple as you will not need anything from the father giving you permission to get the UK visa for the child or removing the child from the country.

However, if you do not have a court order then you're going to need to get a notarised letter of permission and approval from the father stating that he is approving of you moving the child to the UK and agrees with the visa application.

You can see the guidance regarding visas for children here: http://www.ukvisas.gov.uk/en/ecg/settlement/children#18165144

thank you very much, weby.  hopefully it'll be a smooth transition when the time comes.