Was the attack the work of rogue Russia security agents or a chilling message from Putin?

For a man who lived in a modest semi-detached house in a cul-de-sac in the genteel cathedral city of Salisbury, Sergei Skripal had a very immodest past. Some reports suggest that the former officer with Russia's military intelligence service, the GRU, shared with MI6 the identities of as many as 300 Russian agents during his time as a double agent.

At his trial, the Federal Security Service( FSB, the successor to the KGB) compared Skripal to Oleg Penkovsky, who was executed in 1963, and who history records as one of western intelligence's most valuable assets.

After his release in 2010, in the largest snoop swap since the end of the cold war, Skripal would have been all too aware of how his colleagues viewed him. Many in the FSB are fond of quoting the motto of Smersh, Stalin's counter-intelligence unit:” Death to snoop .” That he came from the GRU only built things worse.

” The Russian nation is a strange building ,” said Sir Andrew Wood, a former British diplomat to Russia , now an associate fellow at Chatham House.” The FSB is not a monolithic organisation. There are elements within it like the GRU, which is a sort of competitor to the FSB .”

Many within the FSB are ultranationalists. The assassination of a traitor shortly before this week's presidential election would have made a nice gift for one of their most well known alumnus, President Vladimir Putin, who is seeking to win 70% of the vote.

But while Wood has little doubt that the brazen attempted assassination of Skripal, 66, and his daughter, Yulia, 33, an operation using a rare form of nerve agent available to only a few foreign states, can be laid at Russia's door, he questions whether Putin would have sanctioned it directly.

” I don't doubt it had general acceptance from senior heads- that's the system he's made. Since 2012 Russia has been going backwards, rejecting economic reform and better tribunals in favour of renewed country control and repression, a dread of anything that is other. It's the revival of Stalinism and the idea that Russia has the right to predominate its neighbours .”

In this climate, former FSB policemen now working in the murky world occupied by ex-spies feel they can act with impunity.

Whether Skripal had an inkling their own lives was in danger is unclear. There has been supposition in police circles that he received an Osman notice before he was attacked. These are warns handed by the security services to people they fear may be targeted. But Skripal seems not to have made any changes to his lifestyle: scarcely specific actions of someone in fear for their life.

The are also claims that considerable amounts of money were found in his bank account and that mobile phone records connect him to the former MI6 agent who recruited him. Again , none of this can be confirmed.

But quite a lot is known about the agent in question. At the time of writing of Skripal's arrest in 2004, the Itar-Tass news agency reported that the MI6 officer was working in the British embassy in Tallinn and had been responsible for recruiting scores of Russian intelligence assets. According to the FSB, these included a Russian security service officer, Vyacheslav Zharko.

It's at this point that the past and the current collide. The attempted murder of the Skripals has depicted comparisons with the fatal poisoning of the spy Aleksandr Litvinenko, who was on the payroll of the exiled oligarch and Putin critic, Boris Berezovsky.

Litvinenko Litvinenko in intensive care in 2006. Photograph: Natasja Weitsz/ Getty Images

Zharko has said it was Litvinenko who introduced him to the same MI6 agent who recruited Skripal.

” It all started in 2002, when he introduced me to employees of MI6 … They proposed that I provide consulting services to them, for money. The fee was about EUR2, 000 a month, plus expenditures ,” Zharko once explained to a Russian broadcaster.

But Skripal was in a different league from Zharko. He was the main asset reclaimed by western intelligence when, along with three others, he was released in 2010 in exchange for 10 Russian agents, including Anna Chapman, the British-based spy.

” The exchange was very unusual ,” explained Dr Yuri Felshtinsky, who co-wrote Blowing up Russia with Litvinenko.” It was seen as an invitation for Russians to spy for foreigners because it indicated any Russian “re under arrest for” spying in Russia could be exchanged .”

Felshtinsky suggests the Kremlin had little option but to trade Skripal: pressure was mounting from powerful supporters to get the 10 Russian “sleepers” back as quickly as possible.” They knew they were making a mistake by releasing him, but they knew they would have a chance to kill him afterwards ,” Feltshtinsky said.

But, unlike Litvinenko, Skripal seemed to have opted for a quiet life, maintaining his head down and building no public criticism of Putin. Indeed, all the stories about him last week were of a man who enjoyed a quiet drinking, gambled on scratchcards and studiously visited the graves of his wife Liudmila, and son, Alexander, whose ashes he had had flown back from Russia.

This stimulates the targeting of his daughter all the more shocking.” This is a complete change of the rules of the game and will frighten a lot of people ,” Felshtinsky said. Up to now only someones have been targeted in assassinations suspected of being linked to the Kremlin.

In the UK they include Alexander Perepilichny, a Moscow banker turned whistleblower who died after jogging near his house in Surrey and is suspected of having been poisoned, and Berezovsky, who was determined hanged at his ex-wife's manor in Berkshire.

Former Russian press minister Mikhail Lesin was found dead in a Washington hotel room in 2015. A medical examiner's inquiry and US federal authorities ultimately ruled that he died from falling and making his head after a days-long binge drinking session.

The former Chechen president, Zelimkhan Yandarbiyev, was killed in an explosion in Qatar in 2004 for which three Russians were jailed for life, only to be extradited to their homeland, where they were given a heroes' welcome and apparently freed.

Soldiers Soldiers removing a contaminated ambulance from Salisbury hospital's A& E entrance on Saturday. Photograph: EPA

Their treatment draws comparisons with that of Andrei Lugovoi, the former KGB officer wanted by Britain for Litvinenko's murder , now a legislator and successful tycoon back in Russia.

” Not only do they kill their foes but they also indicate to everybody that a crime is never going to be punished ,” Felshtinsky said.” It[ the murder] might not be discovered, and if it is discovered, even if you are arrested, they'll get you out, and if you are arrested they'll publicly promote you. They are very open, very cynical .”

Some have speculated that Skripal was targeted because he was continuing to mine Russian contacts for information that he was relaying to MI6 and to private intelligence firms.

” Litvinenko was a' gun for hire' once he left Russia ,” said one person who runs a London-based security and hazard analysis firm which has operations in Russia.” There a lot of people like him around. They can earn money acts as consultants to us. Skripal's attempted slaying wasn't subtle. This was about terrorism , not elimination .”

The attack will have alarmed the Kremlin's enemies now residing in the UK. Many arrived between 2008 and 2015 under a now defunct scheme that offered them residency in return for their investing millions of pounds in UK bonds or shares.

Campaigning group Transparency International has found that almost a quarter of all such visas went to Russians who invested virtually PS750m, much of it in London's property market. Private security consultants patrolling their homes in Belgravia and Hampstead are likely to find renewed demand for their services after last weekend's events.

A A Zizzi restaurant in Salisbury remained cordoned off at the weekend. Photograph: Andrew Matthews/ PA

But the Kremlin's allies here will also be concerned. Among MPs, there is a clamour for the full implementation of the so-called Magnitsky Act, something that would allow the government to sanction individuals who are is guilty of corruption and human rights abuse, making them with visa bannings and asset freezes.

The government has also signalled that it could use new powers to target those of Putin's allies who are unable to account for how they came about their wealth.” Transparency International has identified PS4. 4bn worth of properties bought with suspicious wealth in the UK ,” said Duncan Hames, the campaign group's director of policy.” Over a fifth of which is properties bought by Russians. It is clear that the UK has routinely been the choice destination for Russians with suspicious wealth to move and they have had little difficulty doing so, taking advantage of lax regulation and offshore privacy .”

One notable example is Igor Shuvalov, Russia's first deputy PM, whose official wage is PS112, 000. He owns a Westminster property valued at PS1 1.4 m.

Curbing the lifestyle of Putin's rich friends will not give the Kremlin sleepless nights, however.” There may be something fiscal we can do if we know any particular names, but I don't see anything devastating that we could do ,” Wood conceded.

Rather, if Russia's involvement is confirmed, the response may be largely symbolic: the breaking off of diplomatic ties, the refusal to attend key events.” If England decided not to play in the World Cup, that would be a good thing ,” Wood said.

But the UK is unlikely to impose the one sanction that would damage Russia.” European countries, including the UK, have arranged their sanctions policies so far in a way to carefully omit the purchase of Russian gas ,” said Simon Pirani, research fellow at the Oxford Institute for Energy Studies.” In reality, for the UK as well as for most European countries, the realistic alternative sources of imported gas are very limited. American liquified natural gas is in the news, and as far as we can see from our research Russia is going to adopt a pricing policy to protect its European market share from American LNG .”

In Salisbury on Saturday life appeared to have regained some normality, despite the deployment of 180 military personnel to help with the investigation. It is only at the sites known to have been visited by the Skripals- notably the Mill pub and a Zizzi restaurant- that the scene looks like a film set. At each, tents have been erected for investigators to work in and police in protective suits can been find moving around. The police cordons have forced some businesses to close and those that are open have reported slower trading.” It is a shame on the back of a human tragedy ,” said 41 -year-old Claire Singleton, who works in a jewellers.” I feel sorry for the stores that haven't been able to open since the snow .”

Back in Moscow many remain unaware of the narrative.” I don't know anything about that. They lived here, in our build ?” said a bemused middle-aged female at the west Moscow housing estate the Skripals called home for many years.

State media attained only cursory mentions of the attack, including a stark warn to “traitors” not to settle in England because they risked dying in mysterious circumstances. The commentary was echoed by Lugovoi.” The more trash and scum of the Earth that Britain accepts, the more problems it will have ,” he said.

The rhetoric is typical of an increasingly bellicose Russia. Defence secretary Gavin Williamson has said there been a” tenfold increase” in the number of submarines operating in the North Atlantic over the last seven years. Typhoon airplanes from RAF Lossiemouth intercepted two Russian long-range bombers as they approached to within 50 miles of the UK in January.

In addition, Russia's use of fake news, trolls and cyber-attacks confirm the Kremlin's upping of the ante.” What Russia is conducting is a war ,” Felshtinsky said.” It's too expensive for them to start a real war and too dangerous, so they try to find a different form of war, a cheaper form of war. This is the cheapest style to destroy the west .”

Quick guide

Timeline: the poisoning of Sergei and Yulia Skripal