Pressure is growing on Boris Johnson to toughen his stance towards Beijing amid fears over the wellbeing of the Chinese tennis star Peng Shuai, with senior MPs claiming a diplomatic boycott of the Winter Beijing Olympics is now inevitable.

The pressure did not appear to be dissipating after the International Olympic Committee said its president had held a 30-minute video call with Peng. The episode was dismissed by the Conservative MP Tim Loughton, of the influential Inter-Parliamentary Alliance on China as “straight out of the Chinese Communist party playbook”, with the group adding: “The video cannot be considered proof that she is either well or safe.”

Loughton said: “The IOC call does nothing to prove Peng Shuai is safe and well, as anybody who has been paying attention to the CCP’s tactics would know. Xi’s regime disappears people all the time. But incredibly, the IOC is bending over backwards to legitimise these hostage tactics. The IOC should take a leaf out of the WTA’s book, [which] has stood up fearlessly, and should be applauded.

“If people as high profile as Peng Shuai can be disappeared, then goodness knows how many others have fallen foul of the Chinese paranoia. Against this background, lending our stamp of approval to the Beijing Olympics is simply unthinkable.”

Oliver Dowden, the chair of the Conservative party, described the situation as very worrying, adding he welcomed the pressure from the Foreign Office, which over the weekend urged Beijing to offer “verifiable evidence” of Peng’s whereabouts and safety.

The Labour frontbench has tabled written questions asking what representations the Foreign Office has made to the Chinese authorities.

Ministers in the Lords on Thursday will be asked to comment formally by Lord Alton on reports that Liz Truss, the foreign secretary, regards the attack on Uyghur Muslims in Xinjiang as genocide.

Alton is one of the five signatories in a letter calling for a ban on any official UK diplomatic representation at the Winter Olympics, which starts in less than three months.

The letter was signed by Tom Tugendhat, the Tory chair of the Commons foreign affairs committee, Sir Iain Duncan Smith, a former Conservative party leader, and former ministers Tim Loughton and Nusrat Ghani.

Labour in June called for a boycott if by 14 September – the date of the UN general assembly – the Chinese government had not provided the UN proper access to mount an investigation into the treatment of the Uyghur people. Labour MPs said: “The UK government should not send ministers, royal family members or senior representatives to participate in any official duties or ceremonies at the Beijing Olympics.”

“A political boycott by the UK and other states would send a strong signal of the deep global concern with the plight of the Uyghurs and prevent the Games being a PR exercise for the Chinese authorities,” they added.

The British government has taken a firm line opposing all-out sport boycotts, but, after reports that the US will mount a diplomatic boycott, the pressure on the UK to follow suit is growing. Overseas spectators have already been banned by China. Truss has taken a tough line on China but is meeting resistance from No 10 and the Cabinet Office.

Speaking over the weekend, the national security adviser, Sir Stephen Lovegrove, said: “China’s rise is the central geopolitical fact of the 21st century and we have absolutely no desire whatsoever to see that checked at all. Its economic growth is important for us all and important for everybody who lives in China.

“But, equally, I think what we would like to do is to see accommodation and balance asserted within the established rules that act in everybody’s benefit, not just in the benefit of the established hegemons.”

On the issue of the Uyghurs, the UK has repeatedly said that only the international courts can make a determination of genocide. The UK parliament has by contrast voted to describe the repression in Xinjiang as genocide.