The dramatic transformations achieved in TV shows such as Changing Rooms are encouraging homeowners to put superficial changes ahead of more important structural repairs, a new study says.

The report from the Joseph Rowntree Foundation finds that millions of apparently posh pads are hiding "crumbling castles" beneath their well-appointed interiors.

It estimates that up to 1.8million properties could be officially classified as "unfit for human habitation" and the repair bill for these may run to £37bn.

Converted flats are the class of property most in need of repair followed by semi-detached or terraced houses built before 1914, the report said. Most of the run down properties are grouped in inner-city areas in the Midlands and north of England, former mining valleys in south Wales and seaside resorts.

Philip Leather, the report's author and academic at Birmingham University, said television programmes such as Changing Rooms and Home Front stress the impact of an overnight 'makeover'.

He said: "Makeovers are all very well. But more important is the less glamorous task of tackling serious repairs - doing unseen jobs to remedy damp and deterioration."