Proof of sole custody for UK Child Student Visa

[pj123]

I am applying for a student visa for my 13 year Thai niece. Her mother has sole custody as she and the father were never legally married. I have been advised by email by UK Visa & Immigration: 

 

"With regards to your query, we would recommend that the letter is backed up by either a court decision document regarding this or the letter is
certified by a relevant authority. Acceptance is at the discretion of the entry clearance officer. "

 

The letter they refer to is a consent letter from the child applicant's guardian(s) that they consent to the visa application, will pay all costs etc.

 

I discussed this issue with the Swiss Consulate visa section earlier this year and they said they always ask for a proof of sole custody; that there is a document the mother can obtain from her local district office that will certify her status as sole custodian. 

 

Does anyone have any experience of this issue with a UK visa or getting this certificate from a district office? 

 

Thank you

 

 

Edited August 3, 2016 by pj123