Many years ago I worked as a deaf awareness trainer. The people attending the centre I was based in were mostly 50+. These people had received poor education because in "their time" children were told to sit on their hands and not sign. The basic level of literacy was therefore low. This seemed to contribute to "deaf communities" and people marrying within them, because communication with the wider world was so difficult. They would also argue that deaf language and culture was unique and not based on a response to hearing society.
When British Sign Language became more prevalent for the younger community members, it was as a basic language but everywhere used it differently and had their own regional "accents", just like English.
With finger spelling, the deaf people I worked with seemed to do it in abbreviation rather than adhering strictly to the a-z. There was no spellchecking as they went along!
A good current contact for the information you are seeking is:
http://www.britishdeafassociation.org.uk/