Yes, you will need a National Insurance Number to open an ISA account.
Please Note
- If not already listed then you need to enter the National Insurance Number in the Tax ID section of your profile to open a linked ISA account. The system will return an error if you do not.
(Client Portal -> User Menu -> Settings -> Account Settings -> Account Profile -> Profile -> Edit Profile and on the 'Tax Residency' page you may edit the information or remove Tax Residency and add another Tax Residency.)