The big six energy companies in Britain are investing on average only £30 per year from each customer in renewable energy projects. If this continues, the UK may miss its 2020 green targets by 50%.

The findings, compiled for independent green power group Ecotricity, will be published ahead of the government's biggest test yet on commercial confidence about wind power, the Tuesday deadline for bids on the third offshore licensing round.

Ecotricity claims that British Gas parent Centrica has spent £397.3m on renewables over the last five years, only £13.28 per customer per year. E.ON, the German-owned group at the centre of the Kingsnorth coal-fired power station controversy, spent just £210.5m, £5.37 per customer.

"It is a scandal that the average investment in new build by the big six over the past five years does not even amount to £30 per customer. This £30 is roughly what it would take for each company to meet the bare minimum legal obligation to grow renewables by about 1% per year," said Dale Vince, Ecotricity founder.

"While the big six are performing badly, more surprising perhaps is the lack of investment by two green independent companies. With a zero investment in the last five years, they are contributing nothing to the urgent need for new build. By contrast, Ecotricity has invested an average of over £450 per customer a year over the last five years," he added.

The Ecotricity figures show the worst performing of the big six suppliers was EDF Energy, the French group, which is leading the charge to build nuclear reactors in Britain. It is estimated to have invested £89.6m on renewables in this country, or £14.14 per customer. Green Energy and Good Energy have invested nothing, according to Ecotricity, but are purely supply companies which do not generate power, instead buying it on the open market.

Centrica hit back at the findings, saying the Ecotricity figures gave no indication about the level of future spending. "If all the projects we are currently working on come to completion we could spend £3.5bn building 1,500 megawatts of wind power over the next few years," said a spokesman for the group.

The government's renewables advisory board suggests that wind should provide us with a minimum of 31,000MW by 2020, yet 2008 investment levels will generate less than half of the target, 13,849MW, or a 55% shortfall.

Ecotricity says the energy regulator's new green tariffs, issued earlier this month, are likely to make matters worse. Ecotricity will not sign up to Ofgem's guidelines as it predicts they will make green tariffs more confusing and expensive for consumers and will do nothing to encourage energy companies to build new renewable energy.