The average room size in Britain's houses is shrinking fast as householders, egged on by the spate of TV property makeover shows, squeeze in extra bathrooms, studies and utility rooms, according to an official report yesterday.

The Royal Institution of Chartered Surveyors, in its five-year UK housing review, said the average British house has not grown in size, but now has many more rooms.

Other trends identified include more three-storey dwellings, a growing number of loft conversions, an increasing use of bay windows and more garages.

Rics also found that developers have banished the word terraced and now describe row houses as mews homes and townhouses.

A separate report to be published on Monday will highlight how Britain's developers are failing to build the type of homes that people want. Propertyfinder.com will say that 41% of new units being built are two-bed flats or starter homes when only 20% of buyers want such a property.

It says that Britain needs to build 350,000 medium-sized homes every year to plug a shortage of four million three-bed houses.

Government policy is blamed for forcing developers into building high-density apartments, but decreasing room size is attributed to changing social demands.

RICS spokesman Joe Martin said: "We found that even small master bedrooms now tend to have an en-suite shower. People are sacrificing space in relatively small kitchens so they can have a separate utility room.

"We're not quite sure why. It may be from property makeover programmes which tell viewers they must have these things, or perhaps it is from seeing American homes where every bedroom has a bathroom."

The Rics survey found that the long-term decline in the average size of a new-build three-bedroom home in Britain has been halted. But the typical house built today is still 55% smaller than the one built before 1920.

Jim Buckle, managing director of propertyfinder.com said: "Rics research only goes to support our findings that British homes are not meeting people's needs and are too small for homehunters' requirements.

"There are too many smaller homes being built and this oversupply is leading to price declines in the apartment sector while the lack of larger homes is supporting prices in that segment.

"Government policy encouraging the construction of new units, without adequate reference to what people actually want can only make the situation worse."