In an unmarked and undisclosed location in western Ukraine, British and Ukrainian engineers work side by side to fix damaged military hardware, crawling under the chassis of artillery systems and pulling apart the insides of British-donated howitzers.

Until now, the existence of this facility, along with three other similar sites inside Ukraine, has been kept quiet, buried in neutral language to avoid drawing too much attention to the sites, given the sensitivities of all military-linked work inside Ukraine.

However, the Guardian was invited to view the location earlier this week – the first time media have been granted access – during a visit to Ukraine by the UK defence minister Luke Pollard. The facility was an example of Britain doing things that “no other nation has been willing or able to do”, said Pollard.

While there are no British military personnel on site, there are British engineers, contracted by the Ministry of Defence, working in-country. For safety reasons, other countries have often preferred to repair kit outside Ukraine, leading to longer journeys and delays with getting it back to the front.

The facility visited by the Guardian has repair bays for up to 30 vehicles, and is able to fix a number of weapons systems, including British-made AS-90 self-propelled howitzers. The AS-90 was initially planned to be withdrawn from service in the British army in the 2030s, but the decision was made to donate the entire stock of the system to Ukraine over the past few years.

“There are some things that in military times we don’t talk about, but when it comes to industrial partnerships, and the legitimate question of ‘You’ve donated all those AS-90s, what’s happened to them?’… we want to start telling the story,” said Pollard.

He acknowledged that there was risk involved in having the facility inside Ukraine, but said it was a “risk worth taking and managing” in the interest of support for Kyiv. “Any operation or support provided inside Ukraine is clearly going to have a greater risk than if its provided in Poland or anywhere within the Nato article 5 protected area, but it’s precisely this type of support that Ukraine needs to stay in the fight,” he said.

Engineers and technicians from two British companies, BAE Systems and AMS, work alongside Ukrainian colleagues to repair the kit. Many of the Ukrainians hired by the companies were employed previously by Ukrainian military enterprises that have since been damaged or destroyed, and they are now being trained to work with British and other foreign-donated equipment.

Much of the equipment the Ukrainian armed forces are using is now obsolete, meaning a new supply chain for spare parts had to be set up. BAE was involved in the original manufacture of the AS-90 and had access to the technical drawings, but for other systems more creative approaches were required. For the Tunguska, a Soviet-era anti-aircraft platform that is also fixed at the facility, and for Soviet T-72 tanks used by Ukraine, engineers visited the Bovington tank museum in Dorset to look over versions of the vehicles on display there and work out how they could manufacture spare parts in the UK.

Swedish Archer artillery systems are also fixed at the facility, under a cooperation agreement in which the Swedish government pays but the British and Ukrainian engineers do the work. In future, the hope is that the project can expand, to more sites and with more countries involved. “We want one structured, organised approach, where any nation giving equipment has a structure they can plug into,” said Pollard.

Facilities such as this give some insight into how western support to Ukraine might look after a potential peace deal. A so-called “coalition of the willing” has come together, of nations prepared to offer Ukraine support to prevent Russia from attacking again, in the event that Donald Trump’s efforts to bring about a deal between Moscow and Kyiv prove successful.

President Volodymyr Zelenskyy has expressed a desire for any postwar settlement to include a provision that western troops be stationed in Ukraine, and last September the Finnish president, Alexander Stubb, told the Guardian that a coalition of the willing would involve “real security guarantees” that would compel western nations to fight Russia if Moscow violated the ceasefire.

However, the past few years have shown that no western country is ready to go to war in Ukraine, and that calculus is unlikely to change. “We know that our only real security guarantee is going to be a strong Ukrainian army,” said one Ukrainian security source.

Last month, the UK defence secretary, John Healey, said he hoped to deploy British troops to Ukraine in the aftermath of a peace deal, but it is not expected that these troops would engage with Russian forces. “UK forces are not the deterrent, a stronger Ukraine is the deterrent,” said Pollard, hence the focus on the regeneration of Ukrainian hardware as well as on training for Ukrainian troops.

Currently, Ukrainian units used their hardware “to the point of destruction”, he said, and the task after a ceasefire would be to speedily restore all the equipment at the front, something that is not possible when they are in use during daily operations.

“For the UK, one of the key roles in the coalition of the willing is to regenerate Ukrainian armed forces, and to do that we need to have the infrastructure ready to go on day one of the peace,” he said.