Yorkshire slang for an intellecual, drug addled, boozed-up waster, (of which there are many here) or one with pretentions of being such - after the infamous opium guzzling brother of the Bronte sisters, who allegedy wrote the novel 'Wuthering Heights but was too wrecked to notice that his sister published it under her name!
Jim-bob: Yo, Marmaduke. How ya doing?
Marmaduke: Hey, I'm fine mate. How's your Ralph?
Jim-bob: Ah, he's always mashed and on the lash these days.
Marmaduke: Yeah, I heard he's turned into a bit of a Branwell.