What PHD program to choose if my bachelor degree is in Business and Master degree in Computer Science
Doing a PhD is an investment of energies, efforts and time. Choosing it on the base of national legal constraints/requirements is a big mistake, in my opinion. You should choose your PhD according to what you want to study.

My experience is that in UK we don't have such strict checks on your degrees. I am a PhD student in Computer Science and I work everyday with epidemiologists, biologists, statisticians, mathematicians, logicians and also people with business degrees. Cross-disciplinary PhDs here are well considered.

Focus on what you would like to study. Do you want to go deep in business (maybe using your computer science skills) or do you prefer to contribute, hopefully, to computer science? Which one do you feel suits more you? You can start filtering universities, schools and countries only after you find the answers to those questions.

Good luck. ;)