The government is facing renewed pressure over its continued ties to Saudi Arabia following the death of Jamal Khashoggi and the humanitarian disaster in Yemen, after all five main Westminster opposition parties signed an unprecedented joint letter calling for a change of stance.

The foreign affairs representatives for Labour, the SNP, the Lib Dems, Plaid Cymru and the Greens wrote to Jeremy Hunt saying it was “hard to imagine what crime the Saudi government would need to commit” for the UK government to condemn it.

The letter to the foreign secretary, shown to the Guardian, says reports that the dissident journalist was tortured and murdered at the Saudi consulate in Istanbul constituted “the latest in a litany of charges that have been laid before the Saudi regime by the international community”.

Saudi Arabia conceded on Friday that Khashoggi had died at the consulate, but claimed it was the result of a fist fight, an explanation dismissed by a succession of other nations. The UK’s Brexit secretary, Dominic Raab, said on Sunday that it did not seem credible. “There is a serious question mark over the account that has been given,” he said.

Timeline Jamal Khashoggi's death: a Saudi version of events Show Saudi Crown Prince Mohammed bin Salman tells Bloomberg he understands Khashoggi left the consulate after “a few minutes or one hour”. Turkish authorities are welcome to search the diplomatic mission because “we have nothing to hide”, he says. The Saudi consulate in Istanbul tweets that is following up on reports of Khashoggi’s disappearance “after he left the building”. Saudi ambassador Walid bin Abdul Karim El Khereiji denies any knowledge of Khashoggi’s whereabouts, Turkish media says. Riyadh sends investigators to cooperate with Turkey. Consul general Mohammed al-Otaibi tells Reuters all talk of kidnapping is baseless. Otaibi gives Reuters a tour of the consulate. Around midnight, Turkish officials say Khashoggi was killed there. A Saudi statement describes the Turkish allegations as baseless. US ambassador Prince Khaled bin Salman tells Axios the kingdom had nothing to do with the case. Prince Khalid describes allegations against the kingdom as “malicious leaks and grim rumours”. Turkey and Saudi Arabia form a joint working group. Saudi Arabia’s interior minister describes claims in the media that there were “orders to kill [Khashoggi]” as “lies and baseless allegations”. Later, Turkish officials leak details and say he was dismembered with a bone saw. Donald Trump tweets that he had spoken with King Salman, who “denies any knowledge of whatever may have happened”. Saudi-owned al Arabiya TV says 15 men identified by Turkish media on 10 October as part of a hit squad were misidentified “tourists”. Turkish investigators are allowed to search the consulate building. Trump speaks with Mohammed bin Salman, then tweets that the crown prince “totally denied” any knowledge of what happened and Riyadh was launching a thorough investigation. The US secretary of state, Mike Pompeo, says Saudi Arabia has made a “serious commitment” to hold anyone responsible accountable. Saudi Arabia’s public prosecutor says investigations show a fistfight led to Khashoggi’s death. Eighteen people have been arrested and two officials close to bin Salman fired. A Saudi official tells Reuters 15 officials travelled to Istanbul to meet Khashoggi, who had expressed interest in returning home. They threatened to kidnap him; Khashoggi resisted, and was accidentally choked to death during attempts to stop him shouting. An official dressed in Khashoggi’s clothes to make it appear as if he had left the consulate. The body was given to a “local collaborator” who disposed of it. The team then lied to Riyadh to cover up the fact Khashoggi had died.

The letter also cites alleged Saudi war crimes in the conflict in Yemen and the wider crisis in the country, where the UN says up to 14 million people are at risk of famine.

Signed by Labour’s Emily Thornberry, Stephen Gethins of the SNP, Christine Jardine from the Lib Dems, Jonathan Edwards of Plaid Cymru and Caroline Lucas from the Greens, it also mentions the imprisonment of activists, repression over LGBT rights and religion, and the widespread use of capital punishment.

“Given the repeated nature of these violations and atrocities, it is now hard to imagine what crime the Saudi government would need to commit in order for the UK government to condemn them,” says the letter, which was organised by the SNP.

“It cannot be business as usual with a regime that displays blatant contempt and disregard for international law and human rights. The consistent inaction of your government is utterly incompatible with our most basic value as a democracy. We regard it as unacceptable that the UK government not only remains silent, but actively enables this Saudi regime.”

The UK “has continued to supply Saudi Arabia with weaponry which has been used in the devastating war in Yemen, has shamefully rolled out the red carpet for the Saudi crown prince in a state visit earlier this year, and has repeatedly excused their actions in statements before the House of Commons”.

Some concern expressed about the Khashoggi case and other moves were welcome, the signatories wrote, but “the time for rhetoric and photocalls is over. It’s time to act”.

The letter calls for a full condemnation of Saudi Arabia’s “reckless and barbaric” behaviour, a suspension of arms sales for use in Yemen pending an investigation of alleged war crimes, a halt to UK military operations in Saudi, details of diplomatic representations made to Riyadh, and support for an independent inquiry into Khashoggi’s fate.

The Foreign and Commonwealth Office said: “This is a totally inaccurate view. Since Jamal Khashoggi first went missing three weeks ago, the UK has been active in calling for answers and a full investigation into what has occurred. This has included speaking directly to the government of Saudi Arabia on multiple occasions, as well as our international partners.

“The UK has one of the most rigorous arms export licencing policies in the world. The key test for our continued defence exports to Saudi Arabia has always been whether there is a clear risk that items subject to the licence might be used to commit a serious International Humanitarian Law violation. This process was subjected to judicial review last year and the claim against the government was robustly dismissed.”