The Winding Stair in Dublin is great (and not limited to sea food) - they use local produce.
London- Camden Market might appeal to you for Sunday. There are lots of bookshops on / near Charing Cross Road but many of them may be closed on a Sunday afternoon. You could however visit Foyles (also on Charing Cross Road). It independent - they have a couple of branches now in other cities but are not a big chain.
Pubs- depends what you want - the Dog and Duck in Soho is a rather nice Victorian boozer, or the Lamb and Flag in Covent Garden is a good pub, (reputed t be a favourite of Charles Dickens', if that interest you. They do good, pub food (including Sunday Roast, on Sundays) - it is however relatively small and quite popular, so book ahead if you want to eat there. I think they do pre-theatre dining, but allow plenty of time, the times I've eaten there service has been a bit slow, which is fine as long as you are prepared!
Nopi in SoHo is worth considering - it's owned/ run by chef Yotam Ottolenghi, I believe that he has Lebanese roots and so there are those influences on the food, it's all absolutely delicious and they do a very reasonably priced pre-theatre set menu as well as a la carte options.
I've heard very good things about 'Gymkhana' which is an Indian Restaurant in Albermarle street (Mayfair) which gained a Michelin star last year, although I haven't been (yet!)
What are you seeing on the Monday night?