It is not possible to create a sub-account or to maintain more than one portfolio within the same account.
However, you are welcome to open/maintain more than one account with us. You can re-use all the data such as your (e-mail) address and linked bank account to open a new account. There are no costs associated with opening an additional account. Please note that you need to choose a new username for any new investment accounts, as your username is the unique identifier of the account. All other information (such as your linked bank account and email address) can be reused. You can open a new account here.