LONDON - Ninety minutes after resigning as British prime minister on Thursday, Boris Johnson called Ukrainian President Volodymyr Zelenskiy. He told the Ukrainian leader his people had the UK's unwavering support in its fight against Russia, and said Britain would continue to supply vital defensive aid for as long as needed. "You're a hero, Volodymyr," he said, according to an aide who listened to the call. "In this country, everybody loves you."

In the months since Russia invaded Ukraine, Britain has become an important go-between for Zelenskiy, officials in Britain and the United States told Reuters. Part broker, part delivery service, supporting Ukraine has been a crucial part of Johnson's premiership. Ukrainian Foreign Minister Dmytro Kuleba described him as a "true friend of Ukraine" in comments sent to Reuters by his ministry.

Whoever runs Britain in coming months will face important decisions about how to pursue the policy. Johnson told Zelenskiy he still had "a few weeks" to keep the support going, according to the aide. But Britain's leadership will be at a point of transition as Russia is steadily gaining ground in what Moscow calls a "special operation."

Until that last call, Johnson had spoken to Zelenskiy 21 times since the start of the war – once every six days on average. Their conversations often opened with Zelenskiy reading out a "shopping list" of arms, three UK officials with knowledge of the matter told Reuters. The calls could "be very transactional" at the start, one of the officials said.

As an example of the deals that followed, London and Oslo agreed that Britain would send multiple launch rocket systems (MLRS) to Ukraine and receive similar, older equipment from Norway in return that it can modernise, Norway's government confirmed. In May, Ukrainian defence minister Oleksiy Reznikov thanked Britain for its help delivering Denmark's anti-ship missiles.

Britain also recently made an inquiry for 27 Soviet-designed heavy machine guns from Bulgaria, according to a document from state-owned arms company TEREM seen by Reuters. TEREM told Reuters that that deal did not go through.

Britain has pledged 2.3 billion pounds ($2.74 billion) of military support for Ukraine, the second highest level of support after the United States. The official total includes purchases of weapons but not the logistics support that Britain has offered alongside these, Britain's defence ministry said.

Britain played this role because some governments face political opposition to supplying weapons to Ukraine, others need logistical help, and in some cases, have ageing systems that Britain is helping to refurbish, the officials said.

Reuters could not determine how many more such arrangements Britain has helped with; the defence ministry said it works routinely with partners across the globe to procure equipment, but declined further comment.

"The UK has emerged as a leader among allies and partners in providing assistance to Ukraine," U.S. Pentagon spokesman Lieutenant Colonel Anton Semelroth said in a statement to Reuters.

Even though Britain became increasingly involved in diplomacy around the war in Ukraine, Kyiv says its stockpiles of Soviet-era weapons are running low. It says it is using about 6,000 artillery shells a day, while a British defence source said Russia is using about 20,000 rounds a day. Britain's existing stockpile of artillery would run out in days if it was used at the same pace as Russia, the source said.

Analysts say Western countries will soon come to a strategic turning-point, needing to decide whether to double down on arming Ukraine or push for negotiations with Moscow to end the war.

With Britain facing an economic and cost-of-living crisis, it may be challenging to convince the public to keep supporting Ukraine in a war that could last years, said James Rogers, co-founder of London-based foreign policy think tank Geostrategy.

The public initially supported foreign wars like those in Iraq and Afghanistan, but then became disillusioned, opinion polls showed.

"There is undoubtedly a tension every time you spend taxpayers' money," Rogers said. "But the government should try to convince people we either spend the money now to stop Russia in Ukraine, or we face even greater cost somewhere else."

"FINEST HOUR"

Johnson's government, under pressure at home for months before he was forced to quit, was bold overseas. He cast himself as a modern-day Winston Churchill, and in a speech to the Ukrainian parliament in May said the fight with Russia would rank as Ukraine's "finest hour" – invoking Churchill's declaration when Britain faced the threat of being invaded and defeated by Nazi Germany in World War Two.

In an interview with Reuters late last month, he said he wanted Ukraine to be flooded with more Western weapons to stop it running out of Soviet-era artillery.

"So, we supply Ukraine with the material, the equipment, the intelligence so as to make that country in the future if not impregnable, then certainly a place that Russia does not want to attack," he said during a trip to Rwanda for the Commonwealth summit.

London's role helping deliver weapons to Ukraine grew pragmatically, according to British officials.

Britain first noticed the threat of a Russian invasion last April when intelligence from satellite imagery pointed to a Russian troop build-up on the Ukrainian borders, according to a Western official, who spoke on condition of anonymity.

A small number of British officials began planning for that last summer, the official said; in the weeks before the invasion, Britain started delivering NLAWs (Next Generation Light Antitank Weapons), according to the government. These missiles were essential in derailing early Russian incursions into Ukraine, Ukrainian officials have said; its defence ministry celebrated Britain's role providing them in a video on Twitter saying, "Thank you, UK!" alongside images of William Shakespeare and James Bond.

Slowly, two British sources close to the prime minister say, Britain started to help coordinate deliveries and help other countries with logistics. Since April, a coalition of more than 40 nations has been coordinating the aid via an American base in Stuttgart, Germany, but UK and U.S. government sources said many discussions about what type of weapons are needed have been between Zelenskiy and world leaders, as well as Ukrainian defence and military officials.

After Johnson collected Zelenskiy's requirements on their calls, Britain sent military attaches to search for the arms in roughly a dozen countries, including those closest geographically to Russia, a defence source said.

Another defence source added that Britain has been in talks with countries that still use Soviet-era equipment about buying Soviet-era 300 mm rockets for the Smerch system, anti-aircraft missiles, missiles for the BUK SA11 system and spare parts for T72 tanks.

Competition is fierce. British military attaches who tour countries for supplies occasionally bump into their Russian counterparts shopping for the same items, a third British source with knowledge of the matter said. Talks have been held about buying arms with nations further afield.

In the Czech Republic, a senior defence source said that when the Czechs source something that is logistically difficult to transport, Britain helps out, and vice versa. "We do a lot of stuff together," the person said on condition of anonymity. They declined to give details of the weapons delivered.

Bulgaria does not export arms to Ukraine directly, but confirmed Britain is among countries purchasing weapons from there.

"Bulgaria has (a) quite serious arms industry ... At the moment, clients have appeared from Poland, the Czech Republic, England and other European Union countries with purchase orders at very good prices," Bulgarian Prime Minister Kiril Petkov said on the country's national radio in June.

"The industry is booming at present," he said, without specifying whether some of these exports were finally destined for Ukraine.

BORYS JOHNSONIUK

Johnson's role boosted his and Britain's popularity abroad. In a global poll last month, Britain's response to Russia's invasion of Ukraine was voted the best of all the leading Western countries. About 7,000 people from the United States, Britain, France, Germany, Italy, Canada, and Japan participated in the poll, for the annual Munich Security Conference.

In Ukraine, a cafe in Kyiv is selling an apple dessert named the Borys Johnsoniuk, a Ukrainianised version of the prime minister's name. A street in the southern port city of Odesa has been named after the British prime minister; portraits of Johnson depicted as a warrior wrapped in the colours of the Ukrainian flag are on display in a museum in central Kyiv.

The deliveries have led to a closer relationship between Johnson and Zelenskiy, British sources said. While their calls have been mostly about arms procurement, when Johnson and Zelenskiy spoke, one British source said, they also jokingly called NLAWs "in loves" and sang songs with "in love" in the lyrics.

There was no interpreter on their last call, the British aide said: The men spoke in English.

"There is clearly a Johnson touch to this," said Rogers, the analyst. But he said Britain's basic approach is unlikely to change much under a new leader: "The structural approach is probably locked in."

Whoever takes over from Johnson, their next big challenge will be to go beyond purchases of Soviet era material to a new phase, supplying Ukraine with more Western weapons and training its forces to use them.

"If Britain and the West want to keep that support for Ukraine going then we are going to need to move into war production mode," said one of the defence sources.

Britain's foreign minister, Liz Truss, said on June 28 the West needs to "double down" on weapons supplies. She told a parliamentary committee Britain should have started supplying weapons much earlier because it takes months of training before they can be used.

"The best thing we can do now is to ... get more weapons quicker, to get the higher spec weapons and encourage our allies to do that as well," she said.

"We need to increase our industrial capacity." (Elizabeth Piper and Andrew MacAskill reported from London; Tsvetelia Tsvetova reported from Sodia; Additional reporting by Idrees Ali in Washington, Jan Lopatka in Prague; Edited by Sara Ledwith)