Vladimir Putin is a “common criminal dressed up as a head of state” who presides over a mafia regime and who personally authorised the sensational murder eight years ago of the former Russian spy Alexander Litvinenko, a public inquiry heard on Tuesday.

On the first day of the inquiry at the high court in London, Ben Emmerson QC, acting for Litvinenko’s widow, Marina, said the Russian had been the victim of a “horrifying” political assassination. He said Moscow had decided to silence Litvinenko after he threatened to expose links between Putin and Europe’s largest organised crime group.

Two former KGB agents – Andrei Lugovoi and Dmitry Kovtun – allegedly murdered Litvinenko after meeting him on 1 November 2006 at the Millennium hotel in central London. They slipped radioactive polonium-210 into his green tea. That both men were the killers was beyond any “reasonable doubt”, Emmerson said.

In scathing terms, Emmerson suggested that Litvinenko was the victim of a dysfunctional state in which criminals and politicians had merged. “The trail of polonium traces leads not just from London to Moscow but directly to the door of Vladimir Putin’s office,” he said. “Mr Putin should be unmasked by the inquiry as nothing more than a common criminal dressed up as a head of state.”

Tuesday’s long-awaited inquiry follows the collapse of an inquest into Litvinenko’s death last year. The government refused to release its secret files on Litvinenko, who from 2003 worked as an MI6 informant. The home secretary, Theresa May, initially rejected a public inquiry but last summer – following a successful legal challenge by Marina Litvinenko – agreed it could go ahead.

Facebook Twitter Pinterest Alexander Litvinenko in November 2006, while he was being treated at University College hospital in London. Photograph: Natasja Weitsz/Getty Images

The inquiry heard that Lugovoi and Kovtun had poisoned Litvinenko not once but twice. Laying out previously secret forensic evidence, Robin Tam QC, counsel to the inquiry, said that Lugovoi had made three trips to London in the weeks immediately before Litvinenko’s murder, with Kovtun visiting twice.

Two weeks before the ill-fated encounter in the Millennium hotel, the pair met Litvinenko in the Grosvenor Square office of a private security company. Analysis revealed large quantities of polonium on the table and chairs where the three men had sat. Later that evening Litvinenko vomited. Analysis of his hair showed he had come into contact with polonium for the first time that day, October 16 – though in a much smaller dose than the second one that would kill him.

After Litvinenko’s death detectives found polonium in all the hotel rooms where Lugovoi and Kovtun had stayed in London, as well as on Lugovoi’s plane seat from Moscow and in numerous other locations. The trail was like the “path of breadcrumbs left by Hansel and Gretel,” Emmerson said.

On one occasion Lugovoi had tried to “dilute” or “move it [polonium] from one container to another”, leaving massive contamination in his hotel bathroom, Tam said.

In a piece of extraordinary new evidence, Tam also disclosed that Kovtun had confided to an old friend that he had been sent by Moscow to kill Litvinenko. Kovtun travelled to London via Hamburg, where he had lived and worked for six years, and had been employed as a waiter in the city’s Il Porto restaurant.

On 31 October Kovtun met up with his old colleague. They went for a walk in Hamburg’s amusement arcade. Kovtun asked the colleague – identified as D2 – if he knew of any cooks in London who might “put poison into Mr Litvinenko’s food or drink”. “He [Kovtun] said he had a very expensive poison.” D2 knew of a cook in London and passed him his number.

During the conversation Kovtun described Litvinenko as “a traitor with blood on his hands who had deals with Chechnya,” Tam said. The following morning Kovtun flew to London’s Gatwick airport. In the hours immediately before Litvinenko was poisoned Kovtun used Lugovoi’s mobile to phone the cook, identified as C2, according to phone records. The cook told Kovtun he was busy.

Emmerson paid tribute to Marina Litvinenko, describing her in court as a “courageous and brave woman” who had struggled against government “intransigence”. Her only goal had been to uncover the truth about her husband’s murder, he said, in what was a “state-sponsored act of nuclear terrorism”.

Facebook Twitter Pinterest Marina Litvinenko leaves the high court after the first day of the inquiry into her husband’s death. Photograph: Carl Court/Getty Images

The inquiry will invite Lugovoi and Kovtun to give video evidence from Moscow. It is unlikely they will agree. In 2007 the crown prosecution service charged both men with murder. They have protested their innocence. Emmerson dismissed as “absurd” and “ludicrous” claims by Lugovoi that British intelligence had killed Litvinenko, or that the late oligarch Boris Berezovsky was responsible.

Instead, Emmerson laid out possible motives for why the Kremlin had decided to have Litvinenko “liquidated”, as he put it. They included Litvinenko’s long-standing feud with his former spy agency, the FSB, and Vladimir Putin in particular. Litvinenko first met Putin in 1998, when Putin was the FSB’s boss.

This frosty encounter came after Litvinenko blew the whistle on the FSB and revealed that it had given him orders to kill Berezovsky, who would became Litvinenko’s friend and patron. Litvinenko wanted to expose corruption inside the FSB, breaking the agency’s code of silence, the inquiry heard.

In 2000 Litvinenko escaped to Britain with his wife and son, Anatoly, from where he continued to criticise Putin. In the years that followed Putin and the Russian government had formed “an intimate relationship” with Russian organised crime syndicates around the world, Emmerson said. So close were the ties that the two were “effectively indistinguishable”.

Emmerson went on: “A significant part of Russian organised crime is organised directly from the offices of the Kremlin. Vladimir Putin’s Russia is a mafia state.” Litvinenko was murdered for trying to expose this “odious and deadly corruption among the cabal surrounding President Putin,” Emmerson suggested.

In one of two books written in exile, Litvinenko went further, accusing Putin of having links with the Tambov-Malyshev gang, one of Russia’s most powerful organised crime groups. The gang operated in Saint Petersburg in the 1990s, specialising in heroin smuggling, when Putin was the city’s deputy mayor. By the 2000s it had built up extensive operations in Spain.

Facebook Twitter Pinterest Former KGB agent Andrei Lugovoi, pictured in 2006: he and Dmitry Kovtun are accused of poisoning Litvinenko. Photograph: Misha Japaridze/AP

Litvinenko had given useful information to Spanish investigators and intelligence, Emmerson said, and may have testified in a Spanish court about links between Putin and the gang. His whistle-blowing activities and remorseless criticism of Putin made him an inevitable target, he said.

The inquiry heard for the first time Litvinenko’s own chilling deathbed account of what happened in the Millennium hotel. He gave a series of interviews to detectives as he lay in the intensive care ward of University College hospital. He said that he met Lugovoi in the lobby of the hotel. Lugovoi ushered him into the small Pine bar nearby, where they sat in the corner. A silver metal teapot was already on the table.

According to Tam, a waiter in a white shirt and bow tie asked Litvinenko if he would like anything to drink. He declined, worrying about cost. Lugovoi then said: “ There is still some tea left here.” Litvinenko told police: “I poured some tea out of the pot. There was only a little left at the bottom. It was already cold. I swallowed some tea, about three or four times. I didn’t like it for some reason.”

Litvinenko said he realised “something strange” was going on. Kovtun then joined them at the bar, complaining that he had not slept the previous night. Lugovoi left to watch a football match at the Emirates stadium between CSK Moscow and Arsenal; his family had flown to London with him. As he left Lugovoi brought his eight-year-old son to meet Litvinenko.

Litvinenko recalled: “Lugovoi said “This is Uncle Sasha. Shake his hand.” We shook hands and he went.”

Lugovoi has pointed to the presence of his wife and children as proof that he was not a killer, arguing it was improbable he would put them at risk. According to Emmerson, however, the two Russians sent to London to carry out a “political assassination” were unaware of the type of poison they were carrying, or that it was radioactive.

Emmerson said the polonium had been manufactured in Avangard, a closed nuclear facility in Russia. The facility is under the auspices of Rosatom, the Russian atomic energy agency. He said it was highly unlikely an unauthorised group could have gained access to the polonium used to kill Litvinenko, which had a commerical value of “tens of millions of dollars”.

For the Russian state, however, this was a straightforward proposition, he said.

In a letter read after his death Litvinenko accused Putin of personally ordering his murder. There have been questions raised about the letter’s authenticity. Litvinenko’s testimony given to police and revealed for the first time on Tuesday, however, confirms its broad accuracy. He told detectives he had “no doubt whatsoever that this [his murder] was done by the Russian secret service,” with Putin signing off on the order.

“I have no doubt whatsoever that as soon as the power changes in Russia, or when the first officer of the Russian secret services defects to the west, he will say that I have been poisoned by the Russian special services on Putin’s order.”

The inquiry continues on Wednesday and is expected to last 10 weeks.

Who’s who at the inquiry

Sir Robert Owen

The inquiry chairman was initially appointed as coroner to oversee Litvinenko’s inquest, but concluded he could not conduct a “fair and fearless” investigation into who was responsible while the government refused to release intelligence information relating to alleged Russian state involvement, and requested the government grant a public inquiry, which was initially refused. Unlike an inquest, the current inquiry will allow him to consider that evidence in closed session.

Marina Litvinenko

The dead man’s widow, she has fought a dogged and dignified battle to have her husband’s case aired in court after years of delays. After Theresa May refused Owen’s request for a public inquiry in 2013, Litvinenko challenged the decision in court despite having no legal aid, putting her own home at risk. Her barrister paid tribute to her in court as “an extraordinarily brave and impressive woman”.

Theresa May

The home secretary was initially very resistant to granting a public inquiry, admitting in 2013 that a fear of alienating the Russian government was a factor in her decision, although she also cited the cost of an inquiry. Three high court judges ruled in February last year that the home secretary needed “better reasons” for her refusal, and ordered her to think again. An inquiry was announced in July, days after the Russian annexation of Crimea.

Anatoly Litvinenko

The 20-year-old son of the dead man, Anatoly was 12 when his father was murdered, and just six when the family fled Russia in 2000 after his father turned whistleblower on the FSB and subsequently came to fear for his family’s safety.

Now a student of contemporary Russian politics in London, he is expected to give evidence to the inquiry.

Andrei Lugovoi

One of two men whose extradition is sought by the Crown Prosecution Service in connection with the killing. Lugovoi and Dmitry Kovtun met Litvinenko on the two occasions on which police believe he was poisoned, and left a trail of polonium as they travelled from Moscow to London and around the Russian capital. Lugovoi, a former KGB and FSB officer, vehemently denies involvement and has suggested he may have been set up with the polonium by British security services or others. He is now a member of the Russian Duma, meaning he is effectively immune from prosecution.

Dmitry Kovtun

A lower-profile character than Andrei Lugovoi, with whom he is accused of killing Litvinenko, he also denies any involvement in the poisoning. The inquiry will hear evidence that Kovtun asked a contact in Hamburg for the number of a cook in London who could administer the poison, the court was told on its opening day. Like Lugovoi and Litvinenko, he is a former KGB and FSB officer.

Ben Emmerson QC

The high-profile barrister, who specialises in international and human rights, made a dramatic opening statement to the inquiry only a day after he had appeared before the Commons home affairs select committee as counsel to the independent child sex abuse panel.

A deputy high court judge and visiting professor in human rights law at Oxford University, Emmerson also holds the unpaid post of UN special rapporteur on counter-terrorism and human rights. He offered to represent Marina Litvinenko and her son Anatoly pro bono after their backer, the late oligarch Boris Berezovsky, was forced to stop funding the case after he lost a multimillion-pound libel case.

Robin Tam QC

As counsel to the inquiry, the barrister’s role is to assist the chairman by laying out the evidence that he will be called on to consider and offer legal advice, and to lead the questioning of witnesses and interrogation of evidence.

• This article was amended on Wednesday 28 January 2014 to correct a quote from Ben Emmerson QC.