My Muslim friend didn’t even have to sign any document prior to the ceremony. It was done at home.
In the UK, male circumcision is legal, and only requires 2 things:
- That consent is obtained, if the subject is too young to give informed consent, the parent can give it.
- The caveat here is that you have to be able to give parental consent. Simply being the biological father is not enough, an unmarried father is not automatically given "parental responsibility" and must be obtained through courts.
- That the procedure is performed by a "competent person". This is not necessarily a doctor
There also needs to be a consent with both parents. One case in the UK involved a Muslim father wanting to circumcise his son. The mother disagreed and the court upheld the refusal of permission to perform the procedure until the child was of age to decide for themselves.
For many, this is a matter of faith, such as with Muslim and Jewish communities. In Jewish communities, the circumcision (a ceremony called a "Bris" or b'rit milah) and the circumcision is either performed by the father or his representative, but is almost always performed by somebody trained in the procedure, dictated by the "mohel" and are usually physicians...
Either way, written consent is not required, there are no documents to sign, forms to mail in to the government, etc. The only things that need to happen is that parent(s) who have parental responsibility must agree and consent, and that the procedure be performed by a "competent person".