The Sunday Times said that Brown, who is Prime Minister Tony Blair's likely successor, wanted to raise his green profile, and the newspaper also focused on Citigroup's announcement last week that it planned to spend US$50 billion on green projects.

Green companies include those involved in renewable energy, such as solar and wind power, or those who reduce greenhouse gas emissions, such as fuel cell developers.

Shares in Climate Exchange, which runs Europe's main exchange for trading credits for reducing carbon gas emissions, rose 3.6 percent to hit an all-time high of 1605 pence.

At the same time, the price of carbon credits for delivery in Dec. 2008 -- as part of the European Union allowances programme -- rose to a 10-month high.

Companies get one credit when they reduce carbon emissions by one tonne. They can then trade the credits for profit.

Shares in Climate Exchange have more than tripled in five months.

Other companies viewed as important in reducing greenhouse gas emissions, including fuel cell makers, also gained.

Ceres Power, which is developing household boilers that also produce electricity from the gas they use to create heat, rose 3.8 percent.

"On Ceres I've also been told there is going to be a really good announcement, and it might be news of that leaking out," added Bunce, who had not heard details of what the news could be. His firm represents Ceramic Fuel Cells, which is targeting a different part of the fuel cell market. Shares in ITM Power, which wants to replace petrol cars with hydrogen using fuel cells it is developing, also rose 7.4 percent.

The stock is volatile because there are a large number of contracts-for-difference trades as some investors bet the company's technology could be a success and its shares soar while others bet it could fail and the stock collapse.