I am a BSL Interpreter, and have had to study this topic for the last 15 years or so. As such, I hope this answer is useful to you.
Sign languages around the world, have developed in parallel to spoken languages, and therefore the idea that signing could be some 'universal' language is quite absurd. As signing/gesture came before spoken language, it would be more reasonable to assume that the latter should have become the universal language. Sign Language is recognised as a language in it's own right, almost everywhere, except Britain! If the government recognised it now, they would have to commit funds to train interpreters, etc, and that's not going to happen any time soon. Within British Sign Language, there are accents/dialects akin to the spoken language, developing through families, schools and other community groups. For more information, try getting links from the CACDP website, or British Deaf Association website. Hope this is helpful.