The excitement about fuel cells three or four years ago led to unrealistic expectations that drove shares in Porvair above 400p.

In 2001 the company, which has developed the bipolar plates used by United Technologies of the US in its prototype vehicular fuel cells, was able to top up its reserves with a rights issue at 260p.

This time last year the company was expecting to start making commercial volumes of its bipolar plates in the second half. But United Technologies has had to delay its fuel cells programme as the last stage of development is proving tougher than expected.

Porvair now talks a lot less about fuel cells and a lot more about its core filtration businesses. Its filters are routinely used in the aluminium industry, but the company has also highlighted other new areas such as coal gasification.

The technology to produce gas from coal has already been proven. But it has been given added urgency as the US, which has about a quarter of the world's coal deposits, becomes more concerned about the security of its energy supplies.

At 114p, the shares are more or less what they were two years ago. But during that time the company has transformed itself, selling its low margin chemicals businesses to chase growth in materials technologies.

It is now valued for the continuing operations, with nothing factored in for potential sales of bipolar plates. The shares looks like a conservative punt for investors still willing to bet on the fuel cell story. david.blackwell@ft.com