From Ben Reeve-Lewis on the Landlord Law Blog:
One of our notorious landlords, famous for cramming as many people as possible into the tiniest spaces had one of his numerous properties repossessed and bought at auction by a new owner.
Who put builders in to renovate.
As they pulled up the floorboards, they found that people had been living in a basement but there was no access point for it other than the photo you see to the side (actually below). They had been squeezing themselves through the gap.