A group of British lawmakers cancelled a visit to China on Tuesday after one MP who defended Hong Kong's autonomy was not granted a visa, the Guardian newspaper and British and Chinese officials said.
Richard Graham, head of the All-Party Parliamentary China Group and a former diplomat in Beijing and Macau in the 1980s, was refused a visa at the last minute ahead of a three-day trip, the report said.
The delegation had been due to fly out on Tuesday.
Members of the group were scheduled to take part in the UK-China Leadership Forum in Shanghai, a joint initiative with the Chinese Communist party.
"We have raised this with the Chinese government and sought an explanation for their decision to deny a visa," a Foreign Office spokesman said.
"The UK-China Leadership Forum has an important role in UK-China relations," the spokesman said.
At a briefing in Beijing, Chinese foreign ministry spokeswoman Hua Chunying said: "We always welcome visits from British MPs so we may inject more positive energy into our mutual exchanges.
"The cancellation may be due to individual reasons. We hope the British side can do more to enhance our mutual trust and help to promote our bilateral relations," Hua said.
Graham could not be reached for comment.
The delegation was to be led by former government minister and EU trade commissioner Peter Mandelson, who is now a member of the British parliament's upper chamber, the House of Lords.
The Guardian said Graham had been asked by the Chinese embassy in London to make a statement clarifying his thinking on China's policy in Hong Kong after a parliament debate last month.
In the debate, Graham had said that Britain had a duty to uphold the principles of the 1984 joint declaration by Britain and China which paved the way for the return of Hong Kong to China in 1997.
Speaking of the freedoms enshrined in the declaration, Graham said: "If we allow any of those freedoms to be curtailed and if we say nothing about any dilution of Hong Kong's high degree of autonomy, whether deliberate or inadvertent, we risk colluding in Hong Kong's gradual, not immediate, decline."
But he also warned against "any form of car crash with Hong Kong's sovereign master, China".
Student-led pro-democracy protests in the former British colony in recent months have drawn tens of thousands of people but the crowds have shrunk as the movement has struggled to maintain momentum.