BSL is extremely regional, so people in Sheffield use lots of different signs than say Doncaster a few miles away.
Northern Irish Sign Language is also sometimes recognised as being even more dialectically different from the rest - not sure why, whether more ISL influence or something else.
Thanks. Dialects hadn't occurred to me, but I don't think there is any reason why they wouldn't develop. That's rather interesting.
Combination of factors:
Sign language users have historically had small communities based around schools for the deaf, Deaf clubs, and sometimes churches and sports groups. Bear in mind that most deaf people have hearing parents, and that sign was deliberately marginalised by the authorities in favour of oralism (particularly in the UK) since 1880.
Sign languages lacked the homogenising effect of telephone, radio and television until video technology became cheap enough for Deaf people to access. (An hour a week of
Blue Peter See Hear on the BBC
[1] was all you got on broadcast telly until quite recently, and that only started in the 1980s.) Spoken languages have had a century's head start, in that respect.
My own sign is a mixture of Big Gay Yorkshire and Mary Hare, courtesy of my Sheffield BSL tutors and Postman Piers (with the usual SSEishness of Crap Hearing People). I can do London numbers, but they're like starting a bike with the other foot.
[1] Needless to say the majority of BSL you see on telly is the 'London' dialect.