The government has achieved its aim of being the "greenest ever", David Cameron said on Thursday, in his first significant remarks on the environment since reaching office.

"When I became prime minister I said I would aim to have the greenest government ever and this is exactly what we have," he told energy ministers from the world's leading nations at a summit in London.

Cameron said he "passionately believed" the growth of renewable energy was vital to the UK's future. "I believe renewable energy can be among our cheapest energy sources within years not decades," he said. But he warned: "We need to make it financially sustainable."