The British Challenge is administered as an exam. Therefore, only teachers can register candidates and invigilate the competition. If you would like to take part, please request your teacher to make the arrangements.
You could kindly explain that the competition sign-up is simple, the vast majority of participating schools receive at least one award, and that invigilation could be as simple as overseeing you during a lunch-break.
All contact between UKBC and students should be made via teachers (except for in-person events, such as the IBO).