Lost old passport

Hi, I am planning to visit my family in Beijing in January for 3 weeks. Recently I just renewed my British passport. But Home office lost my old passport, in which there were records of my old visas to China. I can find the copy of my old passport details, but I haven't kept the copy of my application records. According to your rules, I have to submitted both of them when I apply entry permit. What shall I do? Please reply with many thanks.