Play based on the beloved 1987 comedy will open at Birmingham Rep next year directed by Sean Foley It is one of British cinema's most quotable comedies: a tale of destitute London actors "drifting into the arena of the unwell" who go on holiday by mistake to the Lake District. Now, the inebriated world of Withnail and I " complete with the notorious super-sized joint called the Camberwell carrot " is destined for the…