a Sportsman's Double

I ended up with an older woman at a club last night. She looked okay for a 57-year-old. We drank a bit, and she asked if I'd ever had a Sportsman's Double. "What's that?" I asked. "It a mother and daughter threesome," she said. I said, "No." We drank a bit more, then she says that tonight was my lucky night. I went back to her place. She put on the hall light and shouted upstairs: "Mum, you still awake?"