Buildings designed to comply with the 2002 Part L of the Building Regulations before 6 April will have only 12 months to start on site before they have to be redesigned to meet the stricter 2006 legislation.

The announcement was made by Housing and Planning Minister Yvette Cooper, who said: "Tackling climate change is one of the biggest long-term challenges we face. This is why on this occasion we need the building industry to comply with the new regulations much more rapidly than normal."

The last time Part L was updated in 2002 the industry had three years from lodging plans in which to commence work under the transitional arrangements.

Building work that has already received full building plans approval where work has not yet started will need to begin before 1 April 2007.

A spokesperson for the OPDM says the finalised version of the Approved Document for Part L will be published very shortly. "We don't have a specific date but it will be in time to meet the 6 April implementation". He adds that the statutory instrument, needed to implement the new regulations, will be released in time for the April deadline - legally this is required 21 days before the new regulations come into force.

The Government has still failed to publish details on complying with the Energy Performance of Buildings Directive. The deadline for member states to turn the directive into law passed on 4 January. An ODPM spokesperson said the timetable would be announced soon.