PRIMARY KEY (nino)
Although the Government tries to ensure that National Insurance Numbers are unique, their uniqueness can not be guaranteed. And you can not guarantee that an input National Insurance Number is free from typos when adding a record for a customer/client. So any database that tries to use a National Insurance Number as a primary key is doomed to fail, eventually.
If a database can not use a National Insurance Number as a primary key, the justification for recording the National Insurance Number at all disappears, unless the database must be used for tax or benefits payments.