China's ambassador to Britain Zheng Zeguang was barred from Britain's Parliament in Westminster over Chinese sanctions on British lawmakers.
The new ambassador was due to attend a meeting of the broadly pro-Chinese all-party group on China, but after a letter from MPs who were subjected to sanctions by China, including the former Conservative party leader Iain Duncan Smith, the Commons Speaker, Lindsay Hoyle, has said the meeting is not appropriate.
The ban was put in place on Tuesday.
The Chinese embassy in London described the postponement of the meeting as a "despicable and cowardly" act.
So, what happened and why could it lead to UK-China ties worsening.
China imposes sanctions
In March of this year, China imposed sanctions on nine British politicians, lawyers and an academic for spreading what it said were "lies and disinformation" over the treatment of the mostly Muslim Uighurs.
The sanctions came as the United States, Canada and the United Kingdom joined the European Union to take what they described as "coordinated action" against China to send "a clear message about the human rights violations and abuses in Xinjiang".
The sanctions blacklisted former and current officials in the Xinjiang region " Zhu Hailun, Wang Junzheng, Wang Mingshan and Chen Mingguo " for alleged abuses.
The British Parliamentarians who were singled out by China have been at the forefront of the year-long campaign calling for sanctions against China over the alleged mass rounding up of Muslim Uighurs in Xinjiang.
Among those sanctioned were former Conservative Party leader Iain Duncan Smith, Tom Tugendhat, the chairman of parliament's Foreign Affairs Committee, Nusrat Ghani and Helena Kennedy, a human rights lawyer who sits in the upper house.
The British foreign secretary, Dominic Raab, responding to the Chinese countermeasures, had said: "It speaks volumes that, while the UK joins the international community in sanctioning those responsible for human rights abuses, the Chinese government sanctions its critics."
British prime minister Boris Johnson also showed his solidarity. "The MPs and other British citizens sanctioned by China today are performing a vital role shining a light on the gross human rights violations being perpetrated against Uighur Muslims," he said.
Letter that led to the ban
Zheng had been due to address the All-Party Parliamentary China Group, which is made up of members from both houses of parliament, on Wednesday. The group is seen as being more sympathetic to Beijing.
Last week, the five parliamentarians who were sanctioned " Sir Iain Duncan-Smith, Tom Tugendhat, Nusrat Ghani, Neil O'Brien and Tim Loughton " wrote to the speaker voicing their concerns.
The two sanctioned peers " crossbencher Lord Alton and Labour's Baroness Kennedy " wrote to the Lord Speaker.
They said as quoted by the BBC: "The sanctions imposed by the Chinese government represent an attack not just on members directly targeted but on Parliament, all parliamentarians, select committees, and parliamentary privilege.
"We should never allow our place of work to become a platform to validate and promote such sanctions.
"We know that this is a view shared by a great many Right Honourable and Honourable Members who will wish their protests to be heard if this visit is to go ahead."
The Commons Speaker Lindsay Hoyle and John McFall, the speaker of the House of Lords, then took the decision to ban the Chinese ambassador.
Speaking on his decision, Hoyle said, "I regularly hold meetings with ambassadors from across the world to establish enduring ties between countries and parliamentarians. But I do not feel it's appropriate for the ambassador for China to meet on the Commons estate and in our place of work when his country has imposed sanctions against some of our members."
Hoyle said he was not banning the Chinese ambassador permanently, but only while the sanctions existed.
Reactions to the ban
Nusrat Ghani, one of the sanctioned British parliamentarians, welcomed the "unprecedented" ban on the ambassador, telling BBC News: "Sanctioning MPs is a direct threat to Parliament and our democracy.
"We will not be silenced nor intimidated by any regime, and our Parliament will not become a tool of propaganda for Chinese Communist Party absurd sanctions."
Another sanctioned MP, Tim Loughton, tweeted: "If the genocidal Chinese regime think they can shut down free speech by parliamentarians in a democracy there are consequences and in this case it is that the Chinese regime must not have a platform in the Mother of Parliaments."
The Times said it was the first time an ambassador had been barred from Parliament.
However, the Chinese embassy didn't welcome the development and was quick to take down the British parliament.
A spokesman said: "The despicable and cowardly action of certain individuals of the UK parliament to obstruct normal exchanges and cooperation between China and the UK for personal political gains is against the wishes and harmful to the interests of the peoples of both countries."
This episode will only worsen relations between China and UK, which have soured in recent years over Beijing's crackdown in Hong Kong, tech giant Huawei, and media reports of human rights abuses against the Uyghur minority in Xinjiang.
At the same time, the UK is also trying to persuade China to endorse its ambitious carbon dioxide reduction targets at the COP26 summit in Glasgow later this year.
With inputs from agencies