I’ve just checked the ten day forecast (Weather forecast and conditions for Charing Cross, Westminster, England - The Weather Channel | weather.com) and it is meant to be dry for the first two days (the third day isn’t available yet).
So anyone who was put off by the weather shouldn’t worry, it should be dry for camping or you could take Klownlife’s spare room (Caravan Sharing at BUC 15 October 3-5.