Nick Clegg believes that David Cameron and George Osborne are being too deferential towards China as they seek to boost British trade links with the country projected to soon be the world's largest economy.

The Liberal Democrats criticised their coalition partners after the prime minister and other senior Tory cabinet ministers declined to meet two of Hong Kong's leading democracy activists.

The deputy prime minister was the only senior minister to meet Martin Lee, the founder of Hong Kong's Democratic party, and Anson Chan, the former head of the territory's civil service, to lobby the UK to speak up for democracy in its former colony.

A source close to Clegg said: "Nick is pretty nonplussed to find himself as the only leading member of the coalition government prepared to uphold the human rights commitments made to Hong Kong by two leading Conservatives – John Major and Chris Patten. The Conservative leadership have become so deferential in their attitude to China that they will not give these assurances themselves.

"The deputy prime minister was happy to meet Anson Chan and Martin Lee but he's dismayed that the Tories won't stand up for democracy in Hong Kong, something every government has done since 1997, as it would have been beneficial for the whole government to be speaking with one voice."

Lee and Chan are visiting Britain after the publication by the Chinese authorities of a white paper which suggested that Hong Kong's governance would be decided by Beijing. Under the Sino–British agreement of 1984, in which Margaret Thatcher agreed to return Hong Kong to Chinese sovereignty in 1997, the former colony is meant to be governed under a "one country, two systems" policy. This is meant to guarantee a certain amount of autonomy for Hong Kong from mainland China.

The democracy campaigners were alarmed when Britain said earlier this month that Hong Kong's constitutional arrangements are working well. Chan told the Financial Times that it was extraordinary that Britain "has seen fit simply to refer to the existence of the white paper without taking a stance on the content".

Clegg said: "The UK remains fully committed to the joint declaration and we will not shy away from defending the principle of 'one country, two systems'. This government believes that the best way to preserve Hong Kong's strengths and to ensure that it continues to prosper is through a transition to universal suffrage which meets the aspirations of the people of Hong Kong.

"The important thing is that the people of Hong Kong have a genuine choice and feel that they have a real stake in the outcome of the 2017 election."