Ay up, why the stress on indefinite articles? | Letters

I’ve been looking out for an example of when the indefinite article, “a”, can legitimately be pronounced “ay”, ie when it’s to be stressed. I found one in your article on the TV series Girls (8 January): “I may be the voice of my generation – or at least the voice of a generation.” What is driving me crazy is that nowadays everybody, including professionals all over the BBC and other channels, says “ay” all the time, instead of th