Peacekeeping role might leave UK with less than half of its regular army ready for deployment elsewhere
If Ukraine and Russia really are edging closer to a temporary ceasefire, then Keir Starmer’s promise to deliver peacekeepers could swiftly become a reality.
And while numerous uncertainties about how and when all this could take place remain, the prospect, first reported by The i Paper in November, and its wider impact on the UK is already concentrating minds.
Defence officials are quick to highlight that without a negotiated peace in place, the precise job and mandate of any hypothetical force is a little up in the air. What exact role the UK would play in a so-called “coalition of the willing” could vary drastically based on how much other allies might contribute to the overall effort.
But defence officials and senior soldiers are clear that if Britain does take a leading role in such a peacekeeping coalition, it would require a significant commitment that would eat into the capabilities and resources of our already stretched armed forces.
‘Little to no room for error’
One senior defence source told The i Paper: “It would almost fully commit the army, when taken along with our other outstanding commitments overseas and protecting the homeland. There would be little to no room for error.”
There are still many hurdles that would have to be crossed before thousands of British boots hit the Ukrainian ground. Vladimir Putin does not appear to in any rush to agree a ceasefire, let alone a peace deal and his red lines could prove to be major obstacles.
The Russian president has reportedly demanded that no foreign troops be deployed to Ukraine, although sources point out that this could be fudged or altered later down the line, once a more permanent peace deal is in place.
However, if a peace deal is agreed, it’s hard to see how any meaningful long-term ceasefire could be guaranteed without a European peacekeeping force. And, as The i Paper has previously reported, it would need a nuclear power like Britain or France playing a significant leadership role for it to have any credibility.
What’s needed for a Ukrainian peacekeeping force?
This is probably the hardest question to answer before an agreement is reached. The job of those troops won’t be clear until they have a mandate from a third party agreed by all sides, including Russia.
This would require fudges on two of Putin’s red lines. He reportedly wants the territory of Ukraine currently under Russian control recognised internationally, as well as no Western troops in Ukraine.
The consensus among British, European and Nato sources is that a buffer zone would need to exist, probably in or around the territory that Russia controls, where peacekeeping forces would be stationed, possibly alongside Ukrainian troops.
“I can see a world where the land Ukraine has already lost becomes a Korea-esque demilitarised zone where European forces could be stationed,” says a British security source.
The level of force those peacekeepers would be allowed to use if a ceasefire were breached would depend entirely on what mandate they have been given. However, it is probably reasonable to assume that Russia would not agree to Western forces being able to strike targets inside Russia or anything else that they might consider escalatory.
That leaves a very small landing zone for agreement on what exactly peacekeepers might be able to do. What might be palatable to all sides, diplomats have told The i Paper, is ground forces from European countries.
That would mean any aggression from Russia towards those troops raises the prospect of full-scale Nato retaliation, therefore making the peacekeepers themselves an effective deterrent. This is where the role of nuclear powers Britain and France would become especially important.
How many troops needed for peacekeeping?
The most obvious question is how many troops will be required for a peacekeeping force that does not directly involve America – and how many soldiers European countries are really willing to commit to this?
Ed Arnold at the Royal United Services Institute think tank says that while we don’t know exactly what would be asked of peacekeepers in Ukraine, the overall size could range from 20,000 to 40,000 European troops with Turkish support.
Starmer’s ambition to play a key and possibly commanding role gives us at least some hints as to what it could mean for British commitments.
Speaking to The i Paper, Arnold says that if Britain is serious about a leading role, “that probably means an armoured brigade of 5,000 is probably a minimum, with a British and French rotating command”.
Servicemen stand at the end of the Steadfast Dart 2025 exercise, involving some 10,000 troops in three different countries from nine nations and represent the largest NATO operation planned this year, at a training range in Smardan, eastern Romania, Wednesday, Feb. 19, 2025. (AP Photo/Vadim Ghirda)
Servicemen from nine Nato countries training in Smardan, eastern Romania, in February (Photo: Vadim Ghirda/AP)
That 5,000 may not sound much in the context of the British Army’s 73,000 regulars. But those troops would need to be rotated if the peacekeeping force is maintained for a long period. That means the actual number could be closer to 15,000 or 20,000, depending on who you ask.
“Typically we say it should be a ratio of one to three for rotation, but that really is the bottom end,” says a senior soldier. “You would want to account for people being deployed, going on leave and training. But that leaves no flexibility. Ideally, you would actually want a ratio of one to four, but that quickly becomes a huge commitment.”
The second most obvious question is what equipment those troops would need to accompany them. “You’re going to need heavy armour to protect them, so tanks and armoured vehicles. Otherwise they are sitting ducks,” says a Nato official.
Other operational essentials would include aircraft capable of performing Intelligence, Surveillance and Reconnaissance (ISR) sorties, so that peacekeepers on the ground would know if they were under attack. They would also likely need missile systems and other surface-to-air defences to eliminate those threats.
Where would this leave Britain?
Starting with the troops, 15,000 to 20,000 soldiers is a big chunk of 73,000 regulars (and 25,000 reservists). That number looks even more stark when, as of January 2025, only 54,695 regulars were fully medically deployable. Obviously, that number is subject to change, but it’s a useful snapshot for understanding the limitations currently facing the British Army.
It would leave the UK with no more than 34,695 regular soldiers – less than half the overall army – that were fully deployable elsewhere
Given the UK’s other commitments to homeland security and overseas deployments, you start to see how quickly those numbers can add up and why there is such widespread concern about Britain’s defensive capabilities.
In terms of equipment, it’s no secret that UK cupboards are a little bare. It’s hard to get exact numbers on things like ammunition supplies or speculate on exactly what equipment British peacekeepers would take with them to Ukraine. But to use one example: Britain has sent a total of 14 Challenger 2 tanks to Ukraine, therefore we can assume these are appropriate for the terrain.
Limited resources
Nato sources say the brigade would need at least one tank battalion, which typically would mean a deployment of 56 tanks. Britain currently has just over 200 of these tanks, according to most recent data.
The situation looks trickier when it comes to reconnaissance. The RAF has a total of 20 aircraft capable of ISR, according to its own figures. They comprise three Rivet Joint, eight Shadow R1, and nine Poseidon MRA1. Without the US, which has over 120 capable aircraft, the job of ISR gathering would be likely to fall to Britain and France. Given the enormous swathes of land involved, this would be very difficult.
These are just two hypothetical examples and of course, there may be other solutions. However, limited resources will be an issue, no matter what. And the demand will not stop with actual frontline equipment like tanks and aircraft. They will require support services such as refuelling and maintenance work in the field, raiding the stock cupboards further.
The grim assessment of one active soldier was: “Deploying a brigade, with additional logistical support? Yeah, we cannot support that.”
Would increased defence spending help?
The uplift in defence spending Starmer has promised would mean billions more invested in the armed force. However, the long lead time for weapons and equipment procurement, and recruitment, means the extra funds would not make much difference to immediate knock on problems that could come from peace keeping in Ukraine.
There are also ongoing arguments about exactly how the armed forces should be expanded. Conscription is off the table for the time being and most inside the forces say the idea of just expanding numbers could create more problems when training time is taken into account.
Some are advocating for more innovative solutions that could involve using extra funding to recruit people with particular skills. For example, private sector experts in AI, and in high-end surveillance tech, could be to be offered financial incentives to join the reserves. “I think it’s fair to say that in some of these high-tech areas, the army is not the place to look for talent right now,” says an MOD official.
And previous experience with British defence procurement suggests that many of the extra billions could be lost on delays and the projects that don’t work out as planned.
Wider dangers
Aside from how exposed Britain forces might feel, having peacekeepers in Ukraine would immediately ask some pretty existential questions of Western security.
“The worst case scenario is that Russia does something, a missile ‘accidentally’ goes off course and kills Nato soldiers, then the alliance doesn’t respond fully,” says Arnold. “That would be both a real battlefield win for Putin and the biggest propaganda win for the West’s adversaries.”
It’s not really clear, however, what the alternative is. Defence officials across Europe are pleased that Starmer is making the case for leading a coalition of the willing. Someone had to, and ideally, it needed to be someone with nuclear weapons to back them up.
Sources in the armed forces all generally tell The i Paper that although the prospect of being so stretched is grim, it is at the very least hammering home how much Britain needs to do to ensure its security. And on the whole, they believe that politicians are now willing to get on with it.
The greatest optimists also believe that if European countries demonstrate in practical terms how willing they are to fight for their own peace, it could soften the heart of a certain man in the White House.
“It might not be full US troops on the ground as such or involvement in the deployment. But if Europe and Ukraine play ball while Russia drags its feet, I can see a situation where America has an additional or expanded base in the region,” says a source familiar with discussions.
As proposals and counter-proposals are made on the future of Ukraine, it seems right that Britain – both the Government and public – is braced for how difficult the coming years might be. However, sources say, that if it ends a land war in Europe and reinvigorates the Nato alliance, including the US, it might, on balance, worth the pain.