You should use Online User Registration at the initial stage during your association with UCL:
When you apply for a programme at UCL: Use OUR to register your personal email address and set a password for it. These credentials allow you to access a small number of online services at UCL prior to receiving an unconditional firm offer.
When you are offered a place at UCL and you accept it:
You can no longer use your personal email address to access online services at UCL. You will be notified by UCL on how you can access the full range of UCL services at that stage.