Moving in with girlfriend, she’s worried about her mortgage if we ever break up. (England)

My girlfriend has recently bought her first house, we are planning on moving in together. We were planning on splitting all bills, mortgage payment etc down the middle. My girlfriend is now worried about what would happen if we were to split up in the future that I could claim a stake in the house. My understanding is that this would only be the case if we were married and were going through a divorce, is that right?