This is from the 2012 case of A Local Authority v AK & Others, https://www.bailii.org/ew/cases/EWHC/COP/2012/B29.html involving a man, AK, who had a brain injury and was declared to have lacked capacity to marry, where the Judge said this:
“This case has thrown up the role of Registrars and of the registration service when a borderline-incapacitated individual presents wanting to marry. It is not a Registrar’s job to assess mental capacity and plainly he or she would be wholly unqualified to do so. If there is doubt in the Registrar’s mind when an individual responds to the standard questions put at the notice-attestation meeting, then the procedure is for the doubt to be referred upwards, first to the local Superintendent Registrar and thereafter, if necessary, to the Office of the Registrar General. In a really tricky case, this could end up with a decision to call for a psychiatric report into capacity. That said, the standard handbook provided to Registrars presently says nothing about the need for mental capacity to contract a marriage and does not mention the Mental Capacity Act 2005. It may be that those responsible for the handbook would wish to consider the advisability of incorporating a paragraph on this, perhaps referring to the basic S3 requirements and summarising the information necessary to be understood and weighed up, with a note on what to do where an individual’s mental capacity to marry may be in real doubt. The experience of this case also suggests that greater emphasis should be laid on the need for the aspiring spouses to be seen separately, not together as happened here.”
If the General Register Office had taken serious action then, my mother would never have been able to marry in 2015 and we would all have been spared the emotional and financial devastation.