Mortgage declined by Nationwide after in person valuation

Hi all,

I've received the below message from my broker today regarding lender's valuation.

"We've received the valuation report back on your clients application. The property has been declined pending Legal clarification that the alterations works which were carried out within the last 10 years have building regulations approval and confirmation of compliance. There are significant sections of single skinned/substandard walls which require upgrading.

Please provide documents to support the building regulations approval and compliance."

What do you make of it and what would you do in this situation? I just feel so disheartened and I've been searching for ages. I forwarded it the Estate Agents and my broker has requested the report from the lender but they usually don't share it.