It is your bank's decision to perform these identity checks and they are responsible for the frequency and the rules that apply to require these checks. We expect payments with a low amount (lower than £30) to be subjected less to identity checks as opposed to higher amount payments.
In the near future, the bank will improve this identity check process by enabling their customers to “whitelist” the merchants like FREE NOW that you trust so that fewer identity checks should be required.
You can contact your bank if you are experiencing too many identity checks when using FREE NOW. Please bear in mind that FREE NOW is also aiming at reducing any unnecessary checks however, the final decision resides with your bank.