The Ivangorod castle by the Narva River. Credit:Ivo Panasyuk Checkpoint Charlie this is not. With the help of a translator (everyone in these parts speaks Russian), I chat to some of those entering Estonian Narva from Russian Ivangorod. A chap in black cap and jeans carries full shopping bags. He complains there were a "lot of jobs" in Soviet times. "Everything was very nice," says Nikolai. He repaired buses. The Baltic states are "inept and stupid", he says. If something went wrong and there was war or conflict, "at least half the local population would go against NATO".

The Narva River divides Estonia and Russia. Credit:Ivo Panasyuk By this stage I suspect he's pulling my leg. No, he's serious. But he's no warmonger. "My relatives and friends are sure that Russia and Estonia should be friends," he says. "If one neighbour is taking the knife, the other takes the axe. No. We should not escalate. And not provoke." Estonian border guard senior specialist Kalmer Janno. Credit:Ivo Panasyuk A woman in a white coat, with striking red dyed hair, comes through next. She is is a proud, patriotic Estonian, she says.

"If NATO or Trump decided to fall back it would be very bad," she says. "The Russian population here is affected by the Russian media, they are watching Russian TV channels. That's why this subject is very big around here." Estonian Stanislav Pupkevich looks over the river towards Russia. Credit:Ivo Panasyuk If you want to annoy a Narvan you need just three words: "Is Narva next?" Next as in: Crimea, eastern Ukraine, Narva. They're sick of it. They're sick of the sanctions hurting local businesses (Narva is much closer to St Petersburg than Estonia's capital Tallinn, so the town depended heavily on trade across the border). They're sick of being side-eyed after crossing the river to visit a family grave or a sightseeing trip to Nevsky Prospekt. Narva was rebuilt by the Soviets after it was flattened in 1944. Credit:Ivo Panasyuk

They're sick of journalists making them the new Cold War flashpoint. But since at least Russia's annexation of Crimea in 2014, military strategists can think of no place more likely to catch an acquisitive Kremlin's eye. Vladimir Cherdakov runs a club in the suburban fringes of Narva. Credit:Ivo Panasyuk And with US President Donald Trump sending mixed messages about his commitment to NATO, and his defence secretary speaking pointedly in Brussels about "moderating" military support for Europe should countries not contribute more to the alliance, the prospect of Russian tanks rumbling across the bridge is not unimaginable. General Sir Richard Barrons paints a picture of a dysfunctional NATO caught strategically on the hop.

Narva's officials are full of praise for their city. Credit:Ivo Panasyuk Sir Richard served in the Balkans, Afghanistan and Iraq during his 36 years in the British army, finishing his career as commander of Joint Forces from 2013 to 2016. He picks Narva as an example of where things could go wrong ("most wars start for bad reasons," he says). The border control between Estonia and Russia. Credit:Ivo Panasyuk "Russia feels seriously aggrieved with the way it's been treated since the end of the Cold War, genuinely sees the enlargement of NATO as a threat … genuinely believes people like me would like to stimulate a colour revolution in Moscow," he says.

He points to the array of precision conventional ballistic missiles in the Kaliningrad enclave, which mean Russia "dominates the air space over the Baltics". The view from Narva Castle in Estonia. Credit:Ivo Panasyuk "There are very sophisticated Russian armed forces within easy reach of Narva. Imagine a moment where we're falling out with Russia, it might be over Syria or Ukraine or Crimea. Well, it's very easy just to send ground forces into Narva and you know … You've locked down the airspace. You've basically broken Article 5 [the NATO defence pact] and say 'come on if you're hard enough'. "At which point the NATO alliance, which have no plan for this and have no resources ready to deal with it would have to mobilise at leisure and fight their way back into the Baltic sphere." On Putin's resolve, he quotes Richard Nixon's autobiography: "Communist leaders believe in Lenin's precept: Probe with bayonets. If you encounter mush, proceed; if you encounter steel, withdraw."

He also paints another scenario – more likely and more insidious. Russians are the "market leaders" in hybrid warfare, he says, combining social media, cyber attacks, propaganda and bought influence to weaken their opponents. "All Russian needs to do [in the Baltics] is promote weakness and instability. Hybrid warfare is very good at weakening alliances, weakening national capacity. And you also know that you could do very small things to breach article 5 and you would bluff the alliance." Since 2014, NATO has been refocusing on its weakness in eastern Europe, after a generation in which it retooled to fight in the deserts of the Middle East. There are regular NATO exercises in the Baltics. Just earlier this year, UK armed forces took part in celebrations for Estonia's Independence Day, ahead of a deployment of 800 troops.

In early March, on a trip to Finland, Estonian President Kersti Kaljulaid insisted that NATO was not preparing for war. "In recent months, many people have got the impression that there is something out of the ordinary going on in the Baltic area," she said. "[NATO] is creating the deterrent that it believes is necessary in the current situation. "For some reason, the notion has spread worldwide that now we may be preparing for something darker. This is absolutely not the case." Many Narvans were not impressed at all by the military display by the British. They wonder, why would you want to provoke the Russians? Why not just be friends? I meet the mayor of Narva, Tarmo Tammiste, in his office – he's a lovely man, generous, welcoming, and proud of his city despite its problems.

Narva, once a beautiful baroque city, was bombed flat in 1944. Under the Soviets it was rebuilt by labourers from across the USSR: Ukrainians, White Russians. Now 97 per cent of the population speak mostly Russian and most of the schools teach a large portion of classes in Russian. From the outside, it would seem they are the perfect population for hybrid warfare of the same model used in Crimea or the Donbas in Ukraine. But though they call themselves Russians, that doesn't mean they want to be Russian citizens, says Tammiste. Quite the opposite, in fact. "They are not Russian Russians, they are Russians in Estonia," he says. "They are proud that they are living here in Estonia."

On cross-border trips, Narvans see first-hand how they're doing much better than their neighbours. The European Union has poured millions into their town, funding a huge refit of the water and sewage systems, building riverside paths and schools. "I have relatives back in Russia and there's a clear difference you see when you go there," says vice-mayor Vyacheslav Konovalov. "Living in Estonia alongside Estonians, you tend to absorb all the good things about life here. Not throwing trash as you go. Tidying up. Which is still a problem back there." Pensioners get more pension in Estonia, he says. Some even save money to send to families across the border. To Narva, Ivangorod is their neighbour, not their enemy. There is a Christmas tradition where the Russian and Estonian versions of Santa Claus meet in the middle of the bridge, then swap cities and distribute lollies to dancing children. Every year the mayor of each town gives a box full of presents to the first child born in the other town.

The main challenge for Narva is not geopolitical, Tammiste says. It's economic. The population is shrinking and when tensions grew between Russia and Estonia it hurt business. The tourism industry was cut by almost half. Most business investment had come from across the border, and this was slashed by sanctions, mistrust and the plummeting rouble. "Some [Russian] companies were even ordered to stop developing businesses," says Konovalov. "All those good things we marketed and put as our selling points, they were all evaporated because of the geopolitical stance. You wouldn't risk your money putting businesses here at this time when everybody talks about 'is Narva next, when is the day?' "We saw the Russians taking the risks and investing money into the region and creating jobs and creating opportunities for young people to stay. So of course we are losing because of these tensions." In the suburban fringes of Narva, club owner Vladimir Cherdakov sits proudly in his dining room and offers me a pancake. The place is not exactly jumping during the lunch hour – I see a bare handful of customers. Born in Narva, Cherdakov is what you'd definitely call a local character. An amateur musician (he presses a copy of his latest CD into my hands), he runs a bunch of businesses around town.

He deplores the effect that sanctions against Russia have had on his town and his business. "Two years ago I opened this place as a restaurant, but I had to turn it around as a nightclub and a general club to hang out, because people in this town don't any more have enough money to buy in big parties or buy good food from the restaurants," he says through an interpreter. "They stay home and they make their own food. So the economic level in the city just dropped in two years. "Every time I see on TV the government decided to cut social benefit, or close a kindergarten or school to cut the budget for some social institution, I see that and I think 'this is happening because of the tensions, because of the sanctions'." He scoffs at the idea of a military threat from Russia. "I don't believe Putin would attack Estonia, never. That's impossible."

And as for hybrid warfare – he says that if, like in Ukraine, nationalists started oppressing Russian-speaking people, insisting they stopped speaking Russian or attacked them, then "something would go really wrong". "But unless something like that happens, no, local people would never go fight the government or NATO forces, never." That said, he has no time for NATO. "Historically, Narva was always a reason for war. A war zone. I don't think it's good for one side to bring in troops and build military bases and bring guns, because the other side will do the same and I don't want to be in the middle of it. There might be a chance that someone will make a bang and it will unleash the hell." On my last morning in Narva, I'm taken for a hazardous walk along the border itself, on the river bank.

For me, my biggest concern is staying upright on the ice. For Estonian border guard senior specialist Kalmer Janno, his main concern seems to be to convey how unconcerned he is by the fact that he's patrolling the frontline against a supposed enemy. "We don't talk about politics. We are professional border guards, we do professional tasks, and both sides understand we have to co-operate," he says, prosaically. His and his Russian counterpart's biggest concern is the river itself. There's good fishing in there. But the water is fast and cold, and every fishing boat must have a licence and keep in contact with the local border station. Their other main concern is endlessly creative smugglers. Once they found a clandestine pipeline running along the bottom of the river, piping cheap vodka from Russia into the EU. He talks to me happily, and a little boringly, about an initiative for cross-departmental co-operation, so police, the border guards, customs and the river rescue squads are all linked together.