Go to a pub and not drink - is this some type of new voyeurism!!
Unfortunately, I've seen it often enough at pubs where music is on - either a paid band or a session.
Last time was at Applecross in Scotland where lots of nice middle-class English families from the campsite decided to bring their kids in to the pub to sample the wonderful Scottish culture in the shape of a young lass on the fiddle and her guitarist boyfriend. They took up all the seats and nobody thought to tell one of the brats to get up and give a seat to the crotchety old grumps (me & mrs) who'd come in to escape the midges.
But really, if the pub isn't very full, nobody's going to bother too much about you taking up space and not drinking or eating anything (it certainly doesn't have to be alcoholic). It won't kill you to buy an orange juice every now and then.
Most good session pubs tend to be small and get very crowded though, and you'll be quite conspicuous if you're occupying space but not contributing

