Building Regulations Completion Certificate by: LCUK Expert
The short answer is that you can sell the house without the completion certificate but in all honestly any buyer would be very foolish to buy a property without the proper paperwork.
If the builders walked off the site before the job was finished than it would seem logical that no final completion was, or could be, issued.
As more people become aware of the building regulations we are seeing more and more house deals breaking down because the vendor cannot supply a final completion certificate. It is a big risk to buy a property with a loft conversion that does not have the proper paperwork.