British Prime Minister Rishi Sunak will visit Kyiv on Friday to launch "a major new package of support" for Ukraine and increase military funding for this financial year to GBP2.5 billion ($3.2 billion), his office said.
The figure is an increase of GBP200 million over the last two years and will ensure the "largest ever commitment of drones," a statement said, adding that he was also due to sign a "historic" security cooperation pact with Ukrainian President Volodymyr Zelensky.
The "totemic agreement" should be the first step towards an "unshakeable hundred-year partnership," said Sunak's Downing Street office.
The extra funding will be targeted at areas including long-range missiles, air defence, artillery ammunition and maritime security, it added.
At least GBP200 million will be spent on "a major push to rapidly procure and produce thousands of military drones for Ukraine, including surveillance, long-range strike and sea drones."
Sunak is also due to meet emergency workers responding to the aftermath of Russian air strikes.
"For two years, Ukraine has fought with great courage to repel a brutal Russian invasion," Sunak said ahead of the visit.
"They are still fighting, unfaltering in their determination to defend their country and defend the principles of freedom and democracy.
"I am here today with one message: the UK will also not falter. We will stand with Ukraine, in their darkest hours and in the better times to come," he added.
The latest commitment takes the UK's support for Ukraine's war efforts to almost GBP12 billion, with Storm Shadow cruise missiles and a squadron of Challenger 2 tanks among the equipment supplied to Kyiv.
British Foreign Secretary David Cameron in November vowed to maintain military support for Ukraine during a surprise visit to Kyiv.
The visit by former prime minister Cameron came as Zelensky said the flow of vital artillery ammunition from Western allies had dropped since the start of the war between Israel and Hamas in October.
"We will continue to give you the moral support, diplomatic support, the economic support, but above all, the military support, that you need not just this year, and next year, but for however long it takes," Cameron said during a meeting with Zelensky.
A top Ukrainian commander recently described the war as a stalemate with and no clear sign of a breakthrough in the frontlines.
