Last ditch attempt for clarity/some concrete answers is going to the council to get categorical answers on the planning permission status.
The work may have been done under permitted development legislation which doesn't require planning permission. The risk is that the work doesn't comply with PD rules. A council would most likely request that a planning application is then made for a lawful development certificate.
When was the work done though? There are time limits on when councils can take enforcement action.
I'd definitely want to see building regs approval though.