When you want time off to do the course, you can just take annual leave, im guessing the police force get about 6 weeks a year, that should be enough for the course and exams.
You could always take unpaid leave, this is up to your employer though.
Also you could take something called a 'career break' again this would be unpaid, but you would have a job to come back to.
You would be better off asking your employer about the options you have as they are the ones that will be giving it to you.