The move comes after pressure from a group of fuel cell companies who are keen to increase the liquidity of their shares and drum up interest from generalist investors.

With more than 50 renewable energy companies on Aim, the junior stock market is a cradle for the development of technologies that might help reduce the global reliance on carbon. But, at present, many retail shareholders and mainstream fund managers are put off investing in these companies by the lack of an index, which would provide a performance benchmark.

"Wind, solar, biofuel and fuel cell companies are all competing for investors on Aim,'' explained Toby Woolrych, chief operating officer of Acta, a fuel cell company. "Most of these companies have little or no revenue and the market needs to find a way to value them.

"The best thing you can do is to put them in one place so that investors can compare them.''

Mr Woolrych, who is leading the push for a renewables index, has the support of other fuel cell companies, including Ceramic Fuel Cells and CMR Fuel Cells.

He met Marcus Stuttard, the deputy head of Aim, last week and got a "very encouraging'' response. "Marcus wanted to know if it's easy to define who is and who is not renewable and it is quite straightforward as Aim companies are generally set up for a single purpose,'' Mr Woolrych added.

A spokesman for the London Stock Exchange commented: "We're always looking at ways to improve the visibility of sectors on our markets but we're probably some way off on this one.''

It may take time to structure an index that works.

Simon Gottelier, from clean energy fund manager Impax, warned that with so many illiquid stocks on Aim, a renewable energy index could be very volatile - offering investors little in the way of a stable benchmark.

The power of the web

THE power of online message boards such as ADVFN and the Motley Fool should never be underestimated.

After a successful message-board-led shareholder revolt at Coffee Republic last year, investors in Transense Technologies mounted another such rebellion at the end of
last week.

They were unhappy about plans for a reverse takeover that would have seen their shareholdings massively diluted. So they organised themselves online and voted down the proposal, putting together an alternative financing package in the process.

Even though he was disappointed at the proposed deal collapsing, Jim Perry, Transense's chief executive, paid tribute to the rebel investors and their use of the internet. "Shareholders can get together much more easily on the internet and they will make it much more difficult for people like me,'' he said.