Pete,
Have you ever heard a really thick Geordie accent? I used to work with a bunch of guys from County Durham and there was one guy that I couldn't understand. For example he would pronounce EVERY LETTER in the word "eighty" so that it came out "a-ig-hu-tee" . It was great fun watching him argue with another guy with a very thick Irish accent. They used to try to tell each other to speak English. We could make out the occasional word now and then but to follow the conversation was impossible.