(Joke) Batchers Vs. Butchers
Solution 1:
My guess is that the entire joke is that its being pronounced incorrectly, the other person saying "sammer padding" (instead of "summer pudding") is teasing the person who says batchers (instead of butchers).
Solution 2:
In many words the letter 'u' is pronounced 'oo' in Northern England, but 'uh' or even 'ah' by southern/RP speakers. The joke is that butcher is not one of these words.