What do you guys mean by "harder"?
Syllabus or Examination?
Because, GCSE has everything that IGCSE offers in addition of another few chapters. GCSE has more material to cover. I'm not sure of how the exam is though.
What makes you think that GCSE is only in UK
? I'm in Bahrain at the moment and there are UK based schools here that offer GCSE instead of IGCSE.