Green energy has come a long way since the 1970s. More accurately, it has travelled the 120 miles that separate the hills of Snowdonia and the Palace of Westminster.

The Welsh connection began 30 odd years ago, when the Centre for Alternative Technology was set up to explore ways of producing energy that didn't damage the planet. In those days it was seen as a mecca for hippies and hobbits. Today, the centre is more likely to be teaching electricians how to install photovoltaic panels. Meanwhile, architects are working on ways to turn the Houses of Parliament into a subsidiary power station, there are plans to site wind turbines along the Thames and senior politicians are racing to become the first to install them in their homes. And for construction folk, making buildings that make energy is becoming as much a part of the job as designing an innovative structure.

The problem is that energy generation is limited by the laws of physics, but regulation has no such constraints. So the announcement this week that mayor Ken Livingstone is to increase the on-site generation requirement for London developments to 20% will bring a huge groan from developers. Most are struggling to meet the 10% threshold - and are doing so only because of the mayor's pragmatic approach, which allows the inclusion of energy efficiency measures as part of the target. At Argent's King's Cross Central scheme, for example, 14 turbines are planned; to hit the 10% target would have required 523. The man with the job of making the system work is Allan Jones, aka the wizard of Woking. During his time as a council official in that town, he managed to retrofit it with 10% of all the UK's photovoltaics and the country's first network of combined heat and power plants. His record is impressive, but to do the same in London would require investment and management of an entirely different order.

The 20% rule would be easier for developers to swallow if more were being done at a national level to harness renewable energy and, above all, to cut the energy used by existing buildings. Unfortunately, the proposed energy labelling scheme for these buildings is in disarray, and while the construction industry and its clients struggle to preserve precious energy on new projects, they do so in the galling knowledge that old ones are leaking it like sieves.

Denise Chevin, editor

No gain, no pain

Don't cheer just yet, but the Treasury's determination to introduce the dreaded planning gain supplement seems to be waning. While housing minister Yvette Cooper is loyally championing the tax, her colleagues across Whitehall are casting around for alternatives (see news). What we can be confident about is that there is going to be some kind of levy - most likely the PGS with extra flexibility. However, given that the number of houses being built is rising at the fastest rate since 1989, it seems a bizarre time to bring in a disincentive to build. One problem is that the Tories have said they won't implement the PGS, so landowners will be tempted to sit on the land until there's a change of government. There's a multitude of other objections too, but for heaven's sake, when the CBI and the Local Government Association see eye to eye on an issue it really is time to listen. The task now is to agree on an alternative.