SNP MP Chris Law has written to the Prime Minister on the eve of the G7 summit and called for him to use the event to “reaffirm the UK’s commitment to being an active player on the world stage”.
The Dundee West MP wrote to Mr Johnson following the plans to slash overseas aid from 0.7 per cent of gross national income to 0.5 per cent.
In the letter, Mr Law said: “The aid budget has been slashed by 40 per cent and life-saving projects around the world have been cancelled.
"I was therefore utterly dismayed by your announcement last weekend that you will commission a new Royal Yacht costing £200 million while you continue to cut aid to the world’s poorest and most vulnerable people amid a global pandemic.
“This new Royal Yacht is reportedly not even wanted by the royal family who are ‘displeased’ by the continual controversy surrounding a project that seems doomed from the get-go.
"Given that this ship is intended to promote British businesses around the world, will you publicly reject the suggestion that funds for its construction and operation should be taken from the aid budget and classed as ODA [Official Development Assistance]?
"Diplomatic missions and trade talks should not come at the expense of the most impoverished and most marginalised people in the world. Every penny taken from the aid budget to fund this project will result in suffering and death.
“The Prime Minister must finally do the right thing, rule out this vanity project and reverse the drastic aid cuts before we start to see the devastating consequences.”
Announced last month, the UK Government intends to build the ship in the UK at a reported cost of up to £200m.
Construction of the new ship is expected to begin as soon as 2022 and it will enter service within the next four years.
The letter comes ahead of the G7 summit starting on Friday where the Prime Minister will meet with the world leaders from the richest democracies – the UK, US, Canada, Japan, France, Germany and Italy, along with representatives of the EU.
Thursday afternoon saw Mr Johnson insist he does not disagree with US president Joe Biden on anything as the pair met for the first time in person.
The meeting has been overshadowed by the ongoing row over Northern Ireland’s Brexit arrangements, which the US say put the Good Friday Agreement at risk.
Ahead of the meeting, Mr Biden said he was looking forward to “affirming the special relationship between the United States and the United Kingdom” – despite Mr Johnson’s dislike of the term to describe the transatlantic partnership because he believes it makes Britain look needy.
The two leaders and their wives – Carrie Johnson and Jill Biden – admired the view over Carbis Bay before their meeting.
Mr Biden said: “I told the Prime Minister we have something in common. We both married way above our stations.”
Mr Johnson responded: “I’m not going to dissent on that one. I’m not going to disagree with you there or indeed on anything else, I think highly likely.”