Gordon Brown should boycott the arrival of the Olympic torch in London this weekend in protest at China's human rights record, according to Liberal Democrat leader Nick Clegg.
The Prime Minister is due to welcome the torch to Downing Street as it is carried in relay around the capital on Sunday by a host of sports stars and celebrities.
But in a letter to Downing Street, Mr Clegg told him: "Serious concerns cannot be swept under the carpet for the sake of ceremonial duties."
And he said that unless China acted to improve the situation in Tibet, Darfur and within its own borders, the PM should boycott all Beijing 2008 related events, including the Games themselves.
Mr Brown has defended his participation, arguing that Tibetan spiritual leader the Dalai Lama had not called for an Olympic boycott and highlighting London's position as the 2012 host city.
However, Mr Clegg wrote: "I understand that on Sunday you will welcome the Olympic torch to London. I urge you to reconsider your participation in this event and indeed any future events to mark the Beijing Games, including the opening ceremony on August 8.
"Recent events in Tibet, broken promises over media freedoms, ongoing human rights abuses and intransigence over the humanitarian catastrophe in Darfur demand a response.
"Serious concerns cannot be swept under the carpet for the sake of ceremonial duties. Unless and until China takes steps to honour the spirit of the Olympics, as laid out in the Olympic Charter, I do not believe that the British Prime Minister can attend the Beijing Games in good conscience."
Mr Clegg said that only if Chinese president Hu Jintao held face-to-face talks with the Dalai Lama, allowed full and free access to foreign journalists, used its influence in Sudan to help the peacekeeping mission in Darfur and ratified an international civil and political rights covenant should UK participation be considered.
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On Thursday, one of the torch-bearers due to carry the Olympic flame across London dropped out in protest at Chinese repression in Tibet. Disabled comedian Francesca Martinez said she felt that taking part would legitimise the continuing violence in Tibet.
