The pub environment has long been linked with entertainment. The modern term “karaoke”, for example, masks a long history of singing in the pub, stretching back into the last century and possibly earlier (and deserving of its own post at a later date). Bar games have also long been popular, and many pubs have teams which compete in local sports competitions.
However, the rise of pub theatres is a relatively recent phenomenon. Of course, pubs have long served theatre patrons. The Shakespeare’s Head (Finsbury EC1, fig. 13) has already been mentioned (in the context of estate pubs, though it replaced an earlier pub on the same site), which serves the nearby Sadler’s Wells Theatre, and as such a bell is rung before the start of the performance and at the end of the interval. The Harlequin (Finsbury EC1), nearby, is similar, and throughout the West End such pubs can be found (although not all are quite so helpful to their patrons as the Shakespeare’s Head in this respect).
Even here at Sadler’s Wells, one can find an example of a pub which incorporates its own theatre, at The Old Red Lion (Finsbury EC1). The theatre on this site (and hence the pub’s rebranding as ‘The Old Red Lion Theatre Pub’) was only created in 1979 and follows a trend during the decade, which began in 1970 with The King’s Head (Islington N1, fig. 14). The theatre here was founded by Dan Crawford, again in an existing Victorian pub, and quickly became a fixture on the scene — if not exactly setting theatrical trends (it always had rather a commercial bent), then certainly fostering young talent who subsequently moved on to the West End mainstream.1
Attaching theatres to pubs has now become rather less unusual a feature outside central London, as a way of supporting local theatrical talent while at the same time ensuring a consistent revenue stream (from the pub). Theatres thus can now be found in such disparate areas as Brockley SE4 (The Brockley Jack) or Battersea SW11 (The Latchmere).
Occasionally these theatre spaces are now more often associated with the growing comedy scene, as at the Hen and Chickens (Canonbury N1, fig. 15). However, just as frequently this can be found in rather more pedestrian function rooms and upstairs bars across the capital.
Flickr set of my theatre pub photos.
 Dan Crawford obituary in The Guardian (15 July 2005).