Despite sharing the same oral language, British, Irish, Australian and American sign language are all completely different languages
“Although the United Kingdom and the United States share English as the predominant oral language, British Sign Language is quite distinct from American Sign Language (ASL) – having only 31% signs identical, or 44% cognate. BSL is also distinct from Irish Sign Language (ISL) (ISG in the ISO system) which is more closely related to French Sign Language (LSF) and ASL.
It is also distinct from Signed English, a manually coded method expressed to represent the English language.
The sign languages used in Australia and New Zealand, Auslan and New Zealand Sign Language, respectively, evolved largely from 19th century BSL, and all retain the same manual alphabet and grammar and possess similar lexicons. These three languages may technically be considered dialects of a single language (BANZSL) due to their use of the same grammar and manual alphabet and the high degree of lexical sharing (overlap of signs). The term BANZSL was coined by Trevor Johnston and Adam Schembri.
In Australia deaf schools were established by educated deaf people from London, Edinburgh and Dublin. This introduced the London and Edinburgh dialects of BSL to Melbourne and Sydney respectively and Irish Sign Language to Sydney in Roman Catholic schools for the deaf. The language contact post secondary education between Australian ISL users and ‘Australian BSL’ users accounts for some of the dialectal differences we see between modern BSL and Auslan. Tertiary education in the US for some deaf Australian adults also accounts for some ASL borrowings found in modern Auslan.
Auslan, BSL and NZSL have 82% of signs identical (using concepts from a Swadesh list). When considering similar or related signs as well as identical, they are 98% cognate. Further information will be available after the completion of the BSL corpus is completed and allows for comparison with the Auslan corpus and the Sociolinguistic Variation in New Zealand Sign Language project . There continues to be language contact between BSL, Auslan and NZSL through migration (deaf people and interpreters), the media (television programmes such as See Hear, Switched, Rush and SignPost are often recorded and shared informally in all three countries) and conferences (the World Federation of the Deaf Conference – WFD – in Brisbane 1999 saw many British deaf people travelling to Australia).
Makaton, a communication system for people with cognitive impairments or other communication difficulties, was originally developed with signs borrowed from British Sign Language. The sign language used in Sri Lanka is also closely related to BSL despite the oral language not being English, demonstrating the distance between sign languages and spoken ones.
BSL users campaigned to have BSL recognised on a similar level to Welsh, Scottish Gaelic, and Irish. BSL was recognised as a language in its own right by the UK government on 18 March 2003, but it has no legal protection. There is however legislation requiring the provision of interpreters such as the Police and Criminal Evidence Act 1984.”