Rishi Sunak will pledge a record £500million military aid package for Ukraine ahead of a meeting with European leaders and Nato’s Secretary-General.
Warning that Russian President Vladimir Putin "will not stop at the Polish border" if his assault on Ukraine is not thwarted, the Prime Minister is set to announce the UK's largest-ever donation of key equipment.
Mr Sunak will travel to Warsaw on Tuesday, where he is set to discuss security co-operation and support for Kyiv in meetings with new Polish Prime Minister Donald Tusk and Nato leader Jens Stoltenberg.
The PM will hold one-on-one talks in Berlin with German Chancellor Olaf Scholz on Wednesday.
"Defending Ukraine against Russia's brutal ambitions is vital for our security and for all of Europe,” Mr Sunak said.
“If Putin is allowed to succeed in this war of aggression, he will not stop at the Polish border.
"I am in Warsaw to deepen ties with our Polish partners and commit critical new military support for Ukraine's defence.
“Ukraine's armed forces continue to fight bravely, but they need our support - and they need it now. Today's package will help ensure Ukraine has what they need to take the fight to Russia.
"The United Kingdom will always play its part at the forefront of European security, defending our national interest and standing by our Nato allies."
The £500 million will be used to send Ukraine ammunition, air defence and drones, as well as supporting engineering and the ramping up of domestic defence supply chains, Downing Street said.
Number 10 insisted the cash was new money from the Treasury reserve and not from existing Ministry of Defence budgets.
It takes the amount of UK military funding for Kyiv to £3billion in 2024/25, and to £7.6 billion since Putin launched his full-scale invasion of Ukraine in February 2022.
The promised equipment includes around 400 vehicles, more than 1,600 strike and air defence missiles, 60 boats and nearly four million rounds of small arms ammunition.
The weaponry will be delivered "as quickly as possible" in response to "specific asks from the Ukrainian government and armed forces," Mr Sunak's official spokesman said.
Defence Secretary Grant Shapps said: "This record package of military aid will give President Zelensky and his brave nation more of the kit they need to kick Putin out and restore peace and stability in Europe.
"The UK was the first to provide NLAW missiles, the first to give modern tanks and the first to send long-range missiles.
"Now, we are going even further. We will never let the world forget the existential battle Ukraine is fighting, and with our enduring support, they will win."
It comes after the US House of Representatives over the weekend approved a critical 61 billion-dollar (£49 million) aid package for Ukraine, following months if stalemate over renewed American support for the war-torn European nation.
Mr Sunak will use his visit to "deepen the relationship with key European partners Germany and Poland," the Prime Minister's spokesman said, adding: "He sees our bilateral security and economic relationship with both Warsaw and Berlin as vital for UK security and prosperity and looks forward to taking that partnership forward."
The trip to the German capital will be his first since entering Number 10, and comes as he has faced pressure to visit senior politicians from one of the UK's most powerful European allies.
