Indications that Britain and the US are secretly preparing to arm resistance fighters in Ukraine in the event of an invasion should raise red flags, and not just of the Russian variety. The effectiveness and wisdom of intervening in other people’s conflicts by proxy, however vital the principle and however seemingly justified the cause, are open to serious question, as much of cold war-era history suggests. Mere mention of the word “resistance” conjures up, in some British minds at least, images of gallant bicyclists in berets, night-time airstrips lit by torches, and furtive wireless operators valiantly plotting to thwart the “Boche”. The recent film Munich: the Edge of War, in which “good” Germans conspire against “bad” ones, is a reminder that things are usually more complicated. Resistance has many faces. Tentative plans under discussion in Washington and London to supply weapons and other military equipment to Ukrainians who object to Kremlin-enforced regime change presuppose that Vladimir Putin, Russia’s president, will launch the long-anticipated invasion and succeed in overthrowing Kyiv’s elected government. Neither eventuality is a given. Putin may continue indefinitely to mess with western heads. An invasion could be repelled. Yet since Joe Biden, the US president, and Boris Johnson, his little trumpet boy, seem convinced the worst will happen – the “biggest war in Europe since 1945”, in the British prime minister’s melodramatic words – it’s only logical to assume the secret talks about post-invasion strategies acquired a new urgency. Jake Sullivan, the US national security adviser, reportedly briefed Congress last week on plans to deliver additional lethal aid to Ukrainians. In truth, it’s not even a big secret. “In discussions with allies, senior Biden officials have made clear that the CIA (covertly) and the Pentagon (overtly) would both seek to help any Ukrainian insurgency,” the New York Times reported last month. Asked recently whether Britain would arm resistance fighters, Johnson replied: “It’s possible, I don’t want to rule this out.” Most public opinion undoubtedly sympathises with the Ukrainian citizens contemplating the destruction of their country’s independence and democracy at the point of a gun. Understandably, many people’s gut instinct would be to resist by all means possible. All the same, officially encouraging what could quickly turn into an extremely violent, long-running, possibly unwinnable struggle requires careful, calm consideration. It’s easy to agitate for a fight when someone else is doing the fighting and when it’s happening a long way away. There’s a moral issue here: if you yourself decline to bloody your hands, should you really be egging on others to do so? If that does not give pause, then think about the practical implications. By helping Ukrainian guerrillas or freedom fighters or people’s militias (the terminology alone is problematic) to kill Russian soldiers, the US and Britain would, in effect, be waging a proxy war against Russia. Russia would know this. Would it passively accept it? Or would it return fire in similarly unpleasant, asymmetrical and hybrid ways? Of course it would. Has Johnson thought about that? Then again, western powers are pretty hopeless at fighting proxy wars via resistance groups. Think of Ronald Reagan’s disastrous Contra war in Nicaragua in the 1980s. Think of the Cuban Bay of Pigs, or how Iraq’s Shias and Kurds were urged to revolt in 1991 by George HW Bush and subsequently betrayed. Saddam Hussein slaughtered them by the thousand. Western politicians, prating about principle then as now, utterly failed them. Resistance groups can be hard to control. They travel unexpected paths. The most notorious example is Afghanistan, where some US-armed mujahideen groups fighting the post-1979 Soviet occupation went on to create the Taliban, who turned on their creators like Mary Shelley’s monster. Perhaps Johnson, unlike the former Texas congressman Charlie Wilson, who was behind the US covert mission, knows what he’s doing. Or is he, in familiar style, already making promises to Ukrainians he cannot and will not keep? Proxy wars often do more harm than good, and western powers are not their only proponents. Consider the misery inflicted upon Yemen’s desperate people by the proxy fight between regional rivals Iran and Saudi Arabia. History is littered with examples of countries where liberators, in overthrowing oppression, became oppressors. Look at Iran, look at Angola. The contrary argument, of course, is that each case is different. Ukraine is different. And so it is, at present. But a western-backed insurgency there could easily morph into civil war, spread to the neighbouring Baltic republics and elsewhere, and become in time a head-on, undisguised, unlimited confrontation with Russia. It’s easy to see Johnson starting such a fight. Knowing him as we do, it’s hard to see him finishing it. Ukraine needs all the support it can get at this moment of enormous, looming trauma. But the best way to help – if it is generally agreed that is the right thing to do – is not to start a potentially endless dirty war of assassinations, bombings, midnight terror, disappearances, bottomless abuses, broken families and broken hearts. If Johnson and Biden truly want to make a difference – and ensure Putin backs off – they should assume the risk themselves, by offering full Nato membership to Ukraine’s government while it still has one. Don’t send out young Ukrainians to fight and die for democracy and freedom while you sit at home, declaring how terrible it all is. Stand up for what you say you believe, or pipe down. Simon Tisdall is a foreign affairs commentator