It is far from being unheard of that people start PhDs 10 or more years after the majority. However, in fast changing subject areas time away can effect your chances. Applying for a PhD is like applying for a job. The supervisor does not just want somebody who they think can pass a PhD, they want somebody who'll churn out some valuable research on their behalf. Don't make excuses for why you went for a career in the police, instead focus on the continuing interest which you have for your subject. If you show suffiecient interest, drive and ability then you shouldn't have a problem.