First time anal

Hi, I'm 15 years old and me and my girlfriend agreed to try anal for the first time in a few weeks time, I have been informed on this website that you want to use a lubricant of some sort but because I live in England I don't know where to get it from, if I can't get it easily without my parents finding out then could I use normal liquid hand soap that my girlfriend has got it her house instead of a branded lubricant. Please may you reply quickly because I need to get whatever I need to use quickly