The panel is formed of leading experts from the worlds of design, the environment, transport and sustainability and was tasked with reviewing developers' proposals, providing expert advice on their work and challenging them to meet the highest standards possible. Developers were grilled on issues ranging from their ability to reduce the carbon footprint of residents and their reliance on cars to the likely "day in the life" of an eco-town resident in 2020.

Many bidders have been praised for their vision and commitment but others are warned that their ideas must be more ambitious or that they lack innovation.

Housing Minister Caroline Flint said: "I have been clear from the start that only those bids that reach the highest possible standards for sustainability can make it through. The Eco-town Challenge panel have played an important role in both providing advice and encouragement to developers on what they have done well, but also challenging them to up their game where there is room for improvement. I'd like to thank the Panel for all their hard work.

"This process was meant to be a challenging ride for the developers, and they need to be open to the creativity of these ideas. Some clearly need to up their game and the ball is now in their court."

John Walker, Chairman of the Eco-towns Challenge Panel, said:
"Our brief was to challenge each proposal in a robust and constructive way, and I think we have done a good job on that front. We have seen much to admire, but in all cases we are challenging the developers to take major steps forward. We want the final eco-towns to be better than the best of the current examples that do exist in the UK and the rest of Europe - clearly there is still a lot of work to do."

Developers now have the opportunity to consider how they plan to respond to these challenges before meeting with the Panel again next month to discuss their work in progress.