Nicholas Watson in Belgrade -

Aleksandar Vucic adopts his gravitas mode: head thrust forward, speaking quietly in short, sharp, bursts of words, Serbia's politician of the moment wants everyone around the restaurant table to know that although he took the tough decision in April to abandon the Serbs in northern Kosovo, he still has their interests at heart.

"We were not informed in advance," Vucic says of the arrest by the EU police force in northern Kosovo on July 29 of two Serbs suspected of the attempted murder of a local official, which promoted the inevitable rock-throwing demonstrations and road barricades. "It's not the way to build confidence and trust - how can we convince our people [in northern Kosovo] to ease the tensions and leave the barricades now?"

Northern Kosovo is proving to be the crucible where Vucic's remarkable transformation from hardline Serbian nationalist to pro-EU, pro-free market libertarian has been played out to an international audience.

In a marathon series of talks brokered by the EU, Vucic and his Serbian Progressive Party achieved in April what has eluded the country since its erstwhile, ethnic Albanian-dominated province of Kosovo unilaterally declared independence in 2008: to get the pockets of Serbs in the north of the country to accept rule from Pristina. Belgrade still - like many other countries, most notably Russia - won't recognise Kosovo as a sovereign nation, but the normalisation of relations with Pristina proved to be enough for the EU to reward Serbia with a date to start talks about joining the bloc.

Vucic described his May visit to northern Kosovo to explain his government's decision to the people there, virtually all of whom regard it as no less than an act of betrayal, as "one of the most difficult days in my political career." But for the powers-that-be in the European capitals, it was a supremely brave act from a 43-year-old who looks set to dominate Serbian politics for the foreseeable future.

Power behind the throne

Fluent in English from his time spent as an 18-year-old student living in London's Gloucester Road, Vucic regales, cajoles and lectures his audience of foreign journalists on the terrace of a swanky restaurant on the bank of the Danube.

That he even turned up is perhaps testament to how powerful he has become. While other ministers begged out of appointments as the fraught negotiations over a reshuffle of the three-party coalition reached their climax, only hours after dumping finance minister Mladjan Dinkic and his small URS party, Vucic was relaxed enough to enjoy a three-hour boozy dinner of fish and seafood, while waving off aides trying to pass on desperate phone calls from the PM and other ministers.

Vucic and his Progressives now rule with Prime Minister Ivica Dacic's Socialist Party. Even though Vucic modestly remains deputy PM, few doubt where the power really lies in the government. Does he want to become prime minister one day? He brushes off the question, airily saying his government has too much to do to think about such trifles.

Indeed it does, given that Serbia has spent the best part of a decade as an international pariah since the Balkan wars of the 1990s and absent from the economic transition the rest of the region went though following the end of communism. But since the Progressives at its first attempt since splitting from the ultranationalist Radical Party in 2008 won both the presidential and the parliamentary elections in May 2012, the party has racked up a series of notable economic achievements to go with the political ones of Kosovo and a high-profile anti-corruption campaign that has already snared the country's richest oligarch, Miroslav Miskovic.

Chief amongst them is foreign direct investment (FDI). So far this year, Serbia has pulled in €400m of FDI, with the central bank predicting the full-year total will exceed €700m. Part of that will be the rabbit out of a hat the government managed to pull by getting the United Arab Emirates' Etihad Airways to save the near-bankrupt JAT Airways (to be newly christened Air Serbia) with a $40m loan and a further $60m of investment in return for a 49% stake and management control.

Again Vucic was at the centre of this, claiming that it was his personal relatonship with the UAE's prime minister, Sheikh Mohammed bin Rashid Al Maktoum, that finally secured the deal. "He is my friend, I met him in Scotland to seal the deal."

Given that Serbia has for some years now been retaking its place as the top investment destination in the region (in the years 2007-12 the total was $12.7bn), Vucic acknowledges that the previous Democratic Party regime of former president Boris Tadic deserves credit for rebuilding the country in the turbulent years after the fall of Slobodan Milosevic in 2000. "I can't say [the Democrats] didn't do anything, it would be a lie - they did things, but not fast enough," he says.

And that's the crux of Vucic: he's a young man in a hurry. His way of speaking, adopting a grave tone when mentioning Kosovo, declaring "I don't care" in a loud voice with a steely stare when asked whether the Serbian people might not sign up to the pace of change he's pushing, are all done in the manner of someone whose character formation is struggling to keep pace with his meteoric rise. Like an extremely tall, slightly baby-faced Travis Bickle practising phrases in the mirror.

A former politician of the Democratic Party of Serbia (DSS) - the only nationalist party still left in the parliament - says he simply can't read Vucic. After all, this is a man who just a decade ago was the de-facto leader of the Radicals while Vojislav Seselj, his "political father", languished in a Hague prison cell on suspicion of war crimes.

Vucic is disarmingly honest about how he, now President Tomislav Nikolic and 19 other radicals deserted Seselj to form the Progressives and embrace a European future for Serbia. "I was wrong, I thought I was doing the best for my country, but I saw the results and we failed, we need to admit that... We cannot remain trapped in the past," he says.

That too sounded a little rehearsed, but you get the feeling it's also true.