Keir Starmer has announced a new deal to give Ukraine access to £1.6billion in UK export finance to buy more missiles.
The Prime Minister said Kyiv will be able to buy 5,000 air defence missiles made in Belfast.
It comes as he announced a four-point plan which includes keeping military aid flowing and economic pressure.
The Prime Minister said lasting peace must ensure Ukraines sovereignty and security.
Europe will keep boosting Kyv’s defence during peace to deter invasion.
And the “coalition of the willing” will guarantee the peace but Europe must do the heavy lifting with strong US backing.
Speaking at a press conference in Lancaster House, the Prime Minister said that “any deal must be backed by strength”.
He went on: “Every nation must contribute to that in the best way that it can, bringing different capabilities and support to the table, but all taking responsibility to act, all stepping up their own share of the burden. So we agreed some important steps today. First, we will keep the military aid flowing and keep increasing the economic pressure on Russia to strengthen Ukraine now.
“Second, we agreed that any lasting peace must ensure Ukraine’s sovereignty and security, and Ukraine must be at the table. Third, in the event of a peace deal, we will keep boosting Ukraine’s own defensive capabilities to deter any future invasion.
“Fourth, we will go further to develop a coalition of the willing to defend a deal in Ukraine and to guarantee the peace. Not every nation will feel able to contribute but that can’t mean that we sit back. Instead, those willing will intensify planning now with real urgency, the UK is prepared to back this with boots on the ground and planes in the air, together with others. Europe must do the heavy lifting.”
Sir Keir earlier urged leaders to step up at a “once in a generation moment” for security in Europe at the start of the defence summit on Ukraine.
Leaders including French President Emmanuel Macron and Nato secretary-general Mark Rutte had gathered at Lancaster House in London to forge a common position on ending the war.
The summit comes after leaders rallied round Ukrainian President Volodymyr Zelensky after his confrontation with Donald Trump at the White House on Friday, which has created a divide between the US and its European partners.
Among those in attendance at the meeting at Lancaster House are Mr Zelensky and Mr Macron as well as German Chancellor Olaf Scholz.
Canadian Prime Minster Justin Trudeau was also at the meeting, alongside Spanish Prime Minister Pedro Sanchez, Italian Prime Minister Giorgia Meloni, and Ursula von der Leyen, the President of the European Commission.
Sir Keir told the gathered leaders that a crowd who welcomed Mr Zelensky with applause ahead of his visit to Downing Street over the weekend was “totally spontaneous”.
