Christian Aid has called upon the UK to help world leaders reach agreement at Rio+20 as it warned that overconsumption in wealthy nations was destroying the environment.

The development agency wants the UK to play the role of “honest broker” at the summit taking place in Rio de Janeiro, in Brazil.

Government leaders and heads of state are meeting to negotiate the next steps in addressing climate change, sustainability and the shift to a “green economy”.

The conference marks the 20th anniversary of the 1992 United Nations Conference on Environment and Development and will also take in discussions on related issues like food security and poverty.

Colombia and Guatemala, with the strong support of the UK, want to see an agreement from leaders to draw up new Sustainable Development Goals.

The Guardian reports that negotiators at Rio have agreed to strengthen the powers of the UN environment programme (Unep).

British Deputy Prime Minister, Nick Clegg, US Secretary of State Hillary Clinton and other national leaders will join the final stage of talks later this week.

There is scepticism from climate campaigners that the conference will see significant progress.

The Prince of Wales criticised the inaction of national leaders in a video message to the summit.

“Like a sleepwalker, we seem unable to wake up to the fact that so many of the catastrophic consequences of carrying on with “business-as-usual” are bearing down on us faster than we think, already dragging many millions more people into poverty and dangerously weakening global food, water and energy security for the future,” he said.

In order for Rio to be a success, Christian Aid said leaders must deliver a plan that will produce a new set of global targets to replace the existing Millennium Development Goals that expire in 2015.

It is also calling for a Rio outcome document that puts a high political priority on the UN Secretary-General’s goal of universal access to sustainable energy and outlines how the private sector will contribute to a fair and sustainable world.

Christian Aid’s senior adviser on sustainable development, Alison Doig, admitted that countries and campaigners looking for radical change “are bound to be disappointed”.

“Christian Aid urges the UK delegation to play the role of creative and honest broker between the two sides, to help Rio deliver a worthwhile outcome which can put the world on a far more sustainable and fair track,” she said.

“More than a billion people live in extreme poverty with even their basic needs unmet while a wealthy minority are destroying the environment with their overconsumption. Humanity cannot afford Rio to be just a talking shop.

“While it can be only a landmark on the path towards a just and sustainable world, it must deliver significant momentum to take us forward.”