Don't use "weren't" and "wasn't" interchangably. 'Anything' and 'nothing', not 'owt' and 'nowt'. There is a 'd' in the middle of 'didn't, it's not 'di't', and wa'eh' is actually said 'water'. These are all the ones I inflict on people, and probably the reason two people this week have said "Oh, you're from the North!" after only one sentence.
Then again you're from London, so I don't know how many of those you actually do anyway. I think accent's a big part of it though; I'd never think of Jarvis Cocker, for example, as posh even though I can't remember ever hearing him use bad English.