they both mean the same thing, it just depends on where exactly you are in the world to determine which is more appropriate to use. As someone already stated, Americans would say "don't have."

none. I think that it's more british to say "I haven't got a pencil", usually in american english we would always say " I don't have ". "I've got" (I have got) means the same thing as "I have". I don't know why. :)

no difference at all :) the sense does not change

No difference, however the first is more common in the US, and the second is more common in the UK.

no difference both of them mean that you dont own or possess a pencil