up until about 4 years ago, it was possible for anyone to apply for parental responsibility. This is particularly relevent if the person applying normally lives with the child and the courts usually grant this barring any really horrible reasons, as you are not trying to change anything with regard to the child. By having parental responsibility, you are simply stating that they can sign an aesthetic form or a apply for a passport on behalf of the child etc etc. Also, multiple people can hold parental responsibility for any child biological and non biological. The natural father will not have parental responsibililty by default unless he was married to the child's mother at the point at which the child was concieved and born, or he lives with the child permanantly.
I'm not sure what the document pinkfizz refers to is, it could be a new legislation, however, it is always advisable to check with a solicitor. There is also a very good book called "Understanding the children's act" which is available from all good book stores, or amazon, it is very informative and I would advise getting it.
good luck.