Green’s Dictionary of Slang

1. a specialist.

1900

Sporting Times 2 June 2/1: At 9 a.m., on Derby day, arrived the Insurance Johnny, accompanied by an eminent specialist, per special train. [...] ‘My dear sir,’ said the spesh.

2. Carlsberg Special Brew, a strong beer popular with alcoholic tramps.

1997		N. Barlay Curvy Lovebox 155: I look up an’ down [...] in my puke-stained blooded up suit. I’m really there. All I need’s a crumpled up can of spesh.
2003		N. Griffiths Stump 86: Eighteen cans of Spesh a day has really only turned him into a louder cunt.