More than 50 world leaders may stay away from next year's Rio+20 Summit in Brazil in order to be in London to mark the Queen's Diamond Jubilee.
Prime Minister David Cameron has already turned down an invite to attend the climate talks in order to remain in the UK to mark the Queen's 60th anniversary of her succession to the throne.
And it is expected all other heads of state from the remaining 53 nations in the Commonwealth will be required to join the Queen in London.
The Jubilee celebrations run from June 2 to 5 and the Rio climate summit runs from June 4 to 6.
The UN-organised meeting will mark 20 years since the Earth Summit of 1992 and is seen as a milestone event for leaders to agree on a sustainable roadmap for the future.
It is understood Environment Secretary Caroline Spelman will head the UK delegation next year in the Prime Minister's absence.
In a report released earlier today, MPs called on David Cameron to attend the summit and lead by example on green issues.
The UK parliament's Environmental Audit Committee, said: "The Rio+20 Earth Summit is a vital chance for world leaders to take action to avert a global environmental crisis.
"The prime minister should lead by example.”
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