Indeed there are a number of pub tours of the West End of London and they do vary in standard but I can highly recommend one and have posted more information below

Covent Garden

For a source of good general information, you will not go too far wrong having a look at The Good Pub Guide and we recommend that as a good read

The Good Food Guide

Here is the tour we are recommending

West End of London Beer Tasting

We found this and thanks to them at SightseeingTours.co.uk