Boris Johnson will seek to put his domestic political difficulties to one side as he meets world leaders for crunch summits in Europe over the coming days.

The Prime Minister will promise further financial support for Ukraine in the form of £429 million (525 million US dollars) in guarantees for World Bank lending and urge allies to commit to supporting Volodymyr Zelensky as the war against Russia drags on.

But his trip to the G7 summit in Germany from Sunday and the Nato meeting in Madrid from Tuesday will keep him out of the country at a time when the Tory party is questioning his leadership in the wake of humiliating by-election defeats and the resignation of party chairman Oliver Dowden.

Mr Johnson was away at a Commonwealth meeting in Rwanda as the by-election results from Tiverton and Honiton and Wakefield came in and he is not expected to return to the UK until after the Nato summit concludes on Thursday, meaning his ability to reassure wavering MPs – or snuff out Westminster plots against him – will be diminished.

But he will hope appearing on an international stage, focusing on the biggest war in Europe since the defeat of the Nazis, will persuade doubters that it is not the time to consider a change in leadership in the UK.

Ahead of the G7 summit at the luxury spa retreat Schloss Elmau in the Bavarian Alps, Mr Johnson said: “Future generations will be awed and inspired by the truly heroic Ukrainian resistance in the face of Putin’s barbarism.

“Ukraine can win and it will win. But they need our backing to do so. Now is not the time to give up on Ukraine.

“The UK will continue to back Ukraine every step of the way, because we know that their security is our security, and their freedom is our freedom.”

The Prime Minister is wary that support for Ukraine among European allies may be wavering as the conflict drags on, meaning Mr Zelensky could be pressured into accepting peace terms which cede large tracts of territory to Vladimir Putin’s Russia.

He would not single out individual nations but said there was a “general sentiment” among some of his fellow leaders.

“If Putin gets away with aggression in Ukraine, if he gets away with the naked conquest of other people’s territory, then the read across for every single country here is absolutely dramatic,” Mr Johnson warned.

Mr Zelensky is due to address the G7 countries – the UK, US, Canada, Japan, France, Germany, Italy – remotely on Sunday.

The Ukrainian government fears it could run out of funding by the autumn unless it is given urgent financial help and Mr Johnson will lobby counterparts to do more, following the example set by the UK.

The loan guarantees provided by the UK will take economic and humanitarian support offered by the Government to £1.5 billion and will cover costs such as public sector wages, and the running of schools and hospitals.

Downing Street said the UK would support Ukraine’s goals of ending the war with a deal which saw Russia’s troops pull out of any territory occupied since the invasion in February.

The Prime Minister’s official spokesman said the two summits “will be the most crucial gathering of world leaders since Putin’s full-scale invasion of Ukraine”.

“The West has come together in recent months to provide the military, financial and political support to Ukraine

“But as it becomes clear this war will not be won overnight by Putin, as he had hoped, but ultimately by Ukraine thanks to their long and continuing resolve – our support needs to enter a new phase.”

The Prime Minister will urge Western allies to increase sanctions “against Putin and his cronies, ensuring they feel the cost of their barbarism”, the spokesman said.

Mr Johnson’s aims also include finding ways to allow Ukrainian grain exports to resume to alleviate global food shortages.

The Prime Minister said there is little hope of sending the Royal Navy to rescue grain from the Russian president’s blockade of Ukraine’s Black Sea ports as he set sights on talks with Turkey to prevent famine being a consequence of the invasion.

Turkey’s Recep Tayyip Erdogan will be at the Nato gathering with Mr Johnson.

At the Nato summit, the Prime Minister will also push for increased defence spending across the alliance and support Sweden and Finland’s bids to join the organisation.