If taking out a SIM Only, this should only require a bank card.
If wanting to take out a phone, this is likely to require Photographic ID (Full Passport, Driving License or Biometric Residence Permit).
Only the lowest cost handsets do not require this.
These proofs vary when purchasing online or over the phone however. The rules above are aligned to an in-store purchase.
A birth certificate is not an accepted form of ID.
