If you have previously sent an invite so that a second person can register on MyCadet, you can withdraw their access at any time.
Click Manage Secondary Contact Access on your MyCadet homepage:
If they have not used the invite to register yet, it will give you the option to withdraw the invite:
If they have already registered, you can withdraw their access by clicking Withdraw Access:
All screenshots and references to persons are taken from the Westminster Training or Development environments. All information contained in these guides has been anonymised and no real personal information is displayed.