Efforts to solve London's deepening housing crisis could be hamstrung by mayor Ken Livingstone's demand that a large proportion of new houses in the capital be fitted with solar panels.
Livingstone has not specified the percentage, but he is calling for the stipulation to be included in the London Plan, due to be ratified in the next few weeks.

Pierre Williams of the House Builders Federation said: "At a time when Livingstone is calling for priority to be given to affordable housing, he is proposing to add £10,000 to the cost of a house. Extra costs affect the viability of sites and can lead to less being developed."

Housing associations are also sceptical. John Hughes, acting director of property and new business for Notting Hill Housing Association, said: "This will undoubtedly make buildings more expensive to build."