I was always mystified as to why 'up' is, supposedly, pronounced as 'ooop' until I worked in London, where there is little difference in vowel pronunciation. e.g. the words in ' Pull, Paul !' sound the same in Thames Estuary English. The idiots also mix up 'bought' and 'brought' ! (a problem never encountered in Leeds or Leith)
If you use the spelling 'up' for the word Southern scum actually pronounce 'ap', you have to resort to the ludricous alternative spelling 'ooop' for the correct pronounciation 'up'.