Ok, here's an update. I went to the British Consulate and found out that my son DOES need a visa to come to England with me when I start my job. They referred me to a website (you aren;t allowed to speak to live humans at the Consulates anymore) for more info and to complete the application. of course, the website is unclear about what form to fill out and what particular visa to apply for if i am going to live there and have a work permit and want my dependent to join me. UGHHHHHHH!!! and to call for clarification costs $3 per minute. this is so frustrating.
bio dad's name is on his birth cert, and i don't know if this means that i have sole custody, since he lives in northern ireland. he has refused to help me in any way. lawyer says that my husband can sign his passport application because my state has a presumtive paternity law, which means that he is legally my son's father, regardless of whose name is on the birth cert. of course, trying to deal with two national governments on this is a nightmare. i can't get the passport without a travel date, and i can't get a travel date until my employer decides when that is, and i can't get the visa without the passport. it's a big mess, and i have feeling that i am going to have to fight tooth and nail to make this all happen.
thanks to everyone who is writing back on this. i feel like the brits are not very supportive or helpful, even though they are eager for me and my other new american co-workers to get there. It's nice to hear advice and support from other americans who have gone through this!