In the study 'Cockney past and present' by William Matthews it's stated that in Cockney speech 'er' was commonly pronounced as 'ar' in the 19th century and that 'sh' was widely substituted for 's'. Whoever the writer was, he'd gone to school in the British Isles because this letter, rough though it is, is set out in the English copybook style taught in British schools, Ireland as well. Also the 'Mr' above the line is seen in most English letters of the 18th and 19th centuries.
I thought both George and his wife were born in Stepney?
I should have been a bit clearer, I meant he was of Irish ancestry. So if I'm right that the autour of the letter was taking the p by using Irishisms, and was the killer of Eddowes, then he most defo knew Lusk and his history. Could that mean by researching Lusk a bit more, we can find out more about the killer? I wonder