I guess you mean pure research verses compulsory classes?
UK is research only so takes 3-4 years. For science PhDs, there may be compulsory classes depending upon the university you are in, but it's only for about 2 hours per week and it's not graded. If you are on a Doctoral Training Program PhD or equivalent, you would have one year of classes that you must pass in order to proceed and 2 rotational lab projects before you start your actual PhD work in the second year. You still have to complete within 4 years total.