The Graduate Admissions website publishes deadlines for all types of postgraduate degrees at the University of Cambridge.
The deadline for Michaelmas 2019 for the full-time PhD course in Criminology (October 2019 start) is 31/5/2019. However, if you require funding, there are earlier deadlines to consider. You can get the funding information here. If you are interested in a part-time PhD course, there are different deadlines.
The Institute of Criminology has several research centres you can choose from. At the VRC we focus on violence prevention, policing, violence trends, violent behaviour in children... to name a few. You can visit our research section here.
If you decide this is the right research hub for you, then you need to contact one of our lecturers (please visit this page) to find out if they can take more students on and what the research field would be as they could be working on different research projects at the same time.
Once you have a PhD supervisor, you need to apply through the Applicant Portal on the Graduate Admissions web page. This website offers information on the whole process, including financial options.