Five opposition parties published a letter on Monday condemning the UK’s continued arms trade with the “murderous regime” of Saudi Arabia and calling the government complicit in Yemen’s devastation.

The letter, published in full by The Independent, is signed by leaders of the Labour Party, SNP, Liberal Democrats, Plaid Cymru and the Green Party’s lone MP.

The UN special envoy for Yemen, Martin Griffiths, is expected in London this week to discuss the redeployment of forces and the opening up of access to humanitarian supplies, especially in the rebel-held strategic port city of Hodeidah.

The city’s fragile truce, negotiated in Stockholm in December, continues to hold, but any failure to implement the deal could lead to even greater devastation in a country that is experiencing what the UN calls the world’s worst humanitarian crisis.

In their joint letter to the foreign secretary Jeremy Hunt, the opposition leaders, including Labour leader Jeremy Corbyn, Liberal Democrat leader Vince Cable and the SNP leader in the Commons Ian Blackford, said the government continues to profit from the conflict through selling arms that it knows are being used to fuel it.

Children suffering from acute malnutrition in Yemen Show all 17 1 /17 Children suffering from acute malnutrition in Yemen Children suffering from acute malnutrition in Yemen Doctors take some blood of Yemeni Yousef Abdullah Bakhit Ali, 13, suffering from severe acute malnutrition. With ongoing and unending conflict in Yemen, humanitarian situation continues to deteriorate across the country Unicef/Huwais Children suffering from acute malnutrition in Yemen A doctor weighs Yemeni baby Yahya Hamoud Ali Al Huzef, 9 months suffering from malnutrition Unicef/Huwais Children suffering from acute malnutrition in Yemen Ali Mohammed Ahmed Jamal,12 years old and suffering from severe acute malnutrition. He arrives with his family at a Unicef supported treatment centre in a hospital in Sanaa Unicef/Huwais Children suffering from acute malnutrition in Yemen A doctor measures the arm of Yemeni Ali Mohammed Ahmed Jamal, 12, who is suffering from malnutrition at a treatment centre in a hospital in Sanaa Unicef/Huwais Children suffering from acute malnutrition in Yemen There are over 400,000 severely malnourished children in need urgent lifesaving assistance in Yemen Unicef/Abdulhaleem Children suffering from acute malnutrition in Yemen Ali Mohammed Ahmed Jamal is weighed Unicef/Huwais Children suffering from acute malnutrition in Yemen A doctor measures the arm of baby Yahya Hamoud Ali Al Huzef Unicef/Huwais Children suffering from acute malnutrition in Yemen Unicef are currently working to reach 275,000 malnourished children with critical life-saving supplies and care for over 5 million people with safe and clean water to stop the spread of life-threatening diseases Unicef/Huwais Children suffering from acute malnutrition in Yemen Yahya Hamoud Ali Al Huzef with his family in his house in the outskirts of the capital Sanaa Unicef/Huwais Children suffering from acute malnutrition in Yemen The country is on the brink of famine and children's chances of survival are becoming slimmer by the day Unicef/Abdulhaleem Children suffering from acute malnutrition in Yemen Ali Mohammed Ahmed Jamal has his arm measured Unicef/Huwais Children suffering from acute malnutrition in Yemen Unicef are currently working to provide nearly 1 million children with vaccines and healthcare Unicef/Huwais Children suffering from acute malnutrition in Yemen Doctors take some blood of Yemeni Yousef Abdullah Bakhit Ali, 13 years old suffering from severe acute malnutrition at a treatment centre in a hospital in the capital Sanaa on November 2, 2018. (Release obtained) With ongoing and unending conflict in Yemen, humanitarian situation continues to deteriorate across the country. There are over 400,000 severely malnourished children in need urgent lifesaving assistance in Yemen. The country is on the brink of famine and childrenâ€™s chances of survival are becoming slimmer by the day. UNICEF are working with partners around-the clock to save children suffering from malnutrition and disease. We are currently working to reach: â€¢ 275,000 malnourished children with critical life-saving supplies and care â€¢ Over 5 million people with safe and clean water to stop the spread of life-threatening diseases â€¢ Nearly 1 million children with vaccines and healthcare â€¢ 9 million people with emergency cash assistance to help families buy basic commodities so they can survive Â© UNICEF/UN0253367/ Huwais Unicef/Huwais Children suffering from acute malnutrition in Yemen Unicef are working with partners around-the clock to save children suffering from malnutrition and disease Unicef/Abdulhaleem Children suffering from acute malnutrition in Yemen Unicef are currently working to provide 9 million people with emergency cash assistance to help families buy basic commodities so they can survive Unicef/Huwais Children suffering from acute malnutrition in Yemen Ali Mohammed Ahmed Jamal is suffering from malnutrition Unicef Children suffering from acute malnutrition in Yemen On 31 October 2018 in Yemen, the Al Thawra Hospital in Hodeidah where children are being treated for severe acute malnutrition. UNICEF Regional Director for Middle East and North Africa Geert Cappelaere visited Yemen from 29 October through 1 November 2018. As of 30 October 2018, over 11 million children â€“ 80 per cent of all children in the country â€“ require humanitarian assistance, due to the impact of the ongoing conflict. Worsening years of underdevelopment, attacks against civilians and civilian infrastructure and lack of salary payments for most civil servants have pushed basic services for children to the brink. Children face food shortages, disease, displacement and an acute lack of access to basic social services. One out of three children in Yemen is at risk of acute malnutrition. Â© UNICEF/UN0253574/Abdulhaleem Unicef/Abdulhaleem

“It is utterly shameful that rather than working with international partners and organisations to bring the conflict to an end, the UK government has instead chosen to pursue a policy of continued arms sales to the Saudi regime that have fuelled the war,” said Mr Blackford, who organised the cross-party letter.

Since the bombing of Yemen began in March 2015, the UK government is believed to have licensed £4.7bn worth of arms to Saudi Arabia.

This figure, the letter said, is “all the more shocking” considering that it overshadows the amount raised by the UN’s Yemen appeal.

The UK recently announced that it was stepping up its efforts to help people in Yemen, bringing the total that the UK has committed since the start of the four-year conflict to £770m.

The letter said it was clear that the government was unwilling to accept any correlation between the sale of weapons to the Saudi government and “the crimes that the regime commits”.

It also questioned the government’s argument that the UK’s close relationship with Saudi Arabia meant it could influence its ally. “The leverage we hold over them must be considerable yet their behaviour and appalling human rights abuses have continued unrestrained,” the letter said.

Whilst a number of countries and international bodies, including Germany, the US congress, the UN human rights council and the European parliament, have all called for a suspension of arms sales, the UK is determined not to pressure its ally to abide by basic human rights laws, the letter claimed.

“It is morally reprehensible that the UK government is not only not considering changing its policy but is actively lobbying other foreign governments, as it did with Germany, to resume weapons sales to Saudi Arabia,” it said.

The foreign secretary last month visited Yemen, becoming the first senior western politician to visit the country since the war broke out in 2015.

Mr Hunt said he had delivered “difficult” messages to the Yemeni government and the Houthi rebels.

“Jeremy Hunt has talked about the need for peace, but the reality is that this war could not be fought without the fighter jets and bombs being produced and sold by arms-dealing governments like the UK,” Andrew Smith from the Campaign Against Arms Trade told The Independent.

Video shows damaged buildings and homes in Yemen village hit by Saudi-led coalition airstrikes

“Whilst humanitarian aid is essential, financial aid alone will not resolve this manmade crisis. The UK must stop supplying arms to the Saudi-led coalition that continues to indiscriminately bomb innocent civilians,” said Jojo Shahvisi, an adviser at War Child UK.

“Profiting from such a disastrous conflict significantly damages Britain’s reputation internationally.”

Yemen’s devastating civil war, which enters its fifth year this week, pits Houthi rebels – who control northern Yemen – against the Saudi-led coalition backing the internationally recognised government.

The UN has documented nearly 18,000 civilian casualties in Yemen – some 10,852 believed to have been victims of Saudi-led coalition assaults.

Its figures say that some 10,000 have lost their lives, however some estimates suggest the death toll may be as high as 56,000 killed since early 2016.

UN experts have accused both sides of committing possible war crimes.

The war has forced the displacement of more than three million people and left most of the population food insecure.

Michelle Bachelet, the United Nations high commissioner for human rights, has warned that despite a recent ceasefire signed in Sweden, children in Yemen continued to be killed and wounded at an alarming rate.

“Since the Stockholm agreement on 13 December, it is estimated that eight children have been killed or injured in Yemen every day,” Ms Bachelet told the UN human rights council last week.

The UN also said that there had been a sharp spike in the number of suspected cholera cases this year, as well as increased displacement in a northern province.