There are definite spatial variations here. I work in the development industry in scotland and 3/4 bedroom detached houses are still preferred in smaller towns and in the large rural developments (farm redevelopments etc) Many developers still have a fear of not being able to shift flats and semis outwith the larger cities of edinburgh, glasgow and aberdeen. The train of thought seems to be that young trendy people, who are probably more likely to buy flats, congregate in the larger 'happening' cities whereas families want smaller towns, rural environment and detached houses with their own garden (defensible space) etc. This is leading to some terrible high density detached developments with houses situated only a couple of metres apart with postage stamps for back gardens. Any thought about producing interesting urban form, green space etc goes straight out the window (unless the planning dept can force it out of them) as they desperately try to lever as many of these detached boxes into a small area to cover the high land values. Unfortunately, due to the high land values many projects become economically unviable if the numbers are lowered due to planning requirements.