if there has been no contact from the father for years, and the child's mother is and has been responsible for his upbringing, then there should be no problems with the sole responsibility, especially if the father is not in the phils..
only time you might get problems with sole responsibility is when the father still has a lot of contact with the child and supports the child, or if the mother works far away from the child and a relative looks after the child.
thou jealous ex's could cause problems just for the sake of it or wanting a pay off, so might be worth not telling him of your plans, just in case he causes problems, and if the father is not in the phils that's even better
you shouldn't have any problems if she has been with the child all his life
http://www.ukvisas.gov.uk/en/ecg/chapter14/ find everythnig you need to know here