The Certified Security Management Professional (CSMP) study program offered by the International Security Management Institute (ISMI) is a UK program that is designed for those with or without prior security work experience. It will cover security fundamentals and in the process perhaps help you to focus on one or two areas within the security industry for further study and concentration. You will discover that a lot of things fall under the big umbrella of Security. These days most security companies and security practioners do not try to be all things to all people.
My advice it to consider which aspect of security is best suited to you from an interest standpoint and from the perspective of long-term business and employment opportunities. You are correct that your educational credentials will be viewed favorably and are applicable. The same can be said of your project management experience. You will find many security requirements are project-based with specific core knowledge that underpins the role or function.