If I had a pint of Guiness for every time I heard an English speaker say "I walked into the pub then everybody started speaking Welsh", I'd probably never be sober ever again. Another variant is the widespread belief that people speaking in Welsh behind you are sure to be talking about you. The technical term for this is paranoia (unless you happen to be an attractive example of the opposite sex, in which case you may very well be the topic of conversation. Lucky you).
Perhaps monoglot English pub-goers should ponder the improbability of their belief. Unless they're entering some remote backwaters pub where no one of sound mind normally ever goes they will find that Welsh speaking pub-goers have plenty of things to talk about without having to wait for a topic of conversation to walk through the door. And perhaps they should consider the fact that Welsh speakers are bilingual, and like all bilingual people the world over they tend to use both languages to some degree in any given sentence (especially when under the influence of a a few pints and a debate about just how evil Jose Morinho is). And perhaps the unwitting would-be eavesdropper should remember that private conversations are just that: private.

I was saddened but not surprised to hear that two lovely girls from Caernarfon on a night out in Blackpool were asked by the staff of the Richmond Hotel -where they were staying- not to speak Welsh to eachother. It isn't the first time that such a thing has happened and it surely won't be the last. But it is strange that after 16 centuries of cohabitation on this island that such xenophobia still exists. 590 years have passed since the last full-on Anglo-Welsh war came to an end, yet cambrophobia is still alive and well amongst our Anglo-Saxon neighbours. Indeed, it is quite evident that the English version of Political Correctness does not quite cover the Welsh (or the "Fucking Welsh" as Tony would say).
Perhaps such establishments as the Richmond Hotel should simply put up a sign saying "No Welsh Here Please" so that decent hardworking Welsh folk can take their custom elsewhere. Or perhaps they should just get a life.