Can my ex partner make a claim on my pension?

My ex-partner (we were never married) is now telling me he has rights to claim part of my pension that I've paid into for several years. We were together for 15 years, and I would say for 5 of those years I was paying in to my pension. Can he do this? I didn't think he would have any rights as we were never married - help! We have been separated for the last 3 years by the way. Thank you!