I think you will find that other telecom providers will ask you for the same proof that you are over 18. They are having to comply with the law.
Personally I would be uncomfortable using any company that is prepared to just take your word for it that you are over 18.
You don't have to send anything, simply entering the numbers from either document on the requisite form will suffice.
If you are not happy to do this then dialling 43432 and following the voice prompts will get you your PAC (transfer code) to move to another network.
These are the only documents that giffgaff wil accept and they will make no exceptions to this policy.
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All networks require Age Verification to lift the Adult Bar.
The difference is that all giffgaff is done on line so these documents are the ones required.
With other major networks you can go into a High Street shop and they will remove it for you.
However if you ring their Call centres they will require proof of age
The request for Age Verification is on the recommendation of OFCOM.
I an certain you need have no worries about enteringthe pPassport or Driving Licence numbers.