Mental Incapacity/memory loss - Spouse unable to deal with tax affairs

My Spouse is receiving Self-Assessment Tax Demands. He refuses to speak about it and blanks out when questioned or presented by it. He applied for a Lasting Power of Attorney for me to be the Guardian and the OPG lost it and failed to process it. He is High Performing Autistic and appears to have blocked the issue from his memory. Please advise how I can help access support to help him resolve what the Tax Demand is about. He was PAYE employment during the period concerned so it may be about investments. We are going into Legal Mediation on Property & Financial Affairs for guidance as the OPG totally failed him. We don't know what to do. I am calling the HMRC line but can't get through.

Hi,

You will need to  obtain the lasting power of attorney, as you will have to send the original to HMRC at HM Revenue and Customs BX9 1AS. With the lasting power of attorney, we can update your husbands records, to reflect that you have the authority to act on his behalf. We can then discuss and hopefully resolve the situation with you. As a valauble document, it would be returned to you.

Thank you.