The poisoned former spy Sergei Skripal was initially reluctant to believe the Russian government had tried to kill him, according to a new book, and despite selling secrets to MI6 was an “unashamed Russian nationalist”.

Skripal struggled to come to terms with his situation following the novichok attack on him and his daughter, Yulia, the author and BBC journalist Mark Urban writes.

The pair were targeted in March and nearly died. When Skripal woke five weeks later from a coma, he faced some “difficult psychological adjustments” – not least the fact that he was at first reluctant to recognise he had been the target of a Kremlin “murder plot”.

As an information war raged between London and Moscow, Skripal recuperated, and sometimes sat in a garden near the main part of Salisbury hospital. Against all predictions, doctors managed to save his and his daughter’s life using “novel therapies”.

Urban’s book, The Skripal Files, is published this week. In it, Urban recalls a series of meetings with Skripal in summer 2017 when the Russian spy was living quietly and apparently safely in an MI6-bought house in Salisbury.

According to Urban, Skripal said he was reluctant to to be quoted directly, explaining: “You see, we are afraid of Putin.” He did not believe he was personally in danger, but wanted to avoid making public statements so Yulia Skripal and his son, Sasha, could visit him freely from Moscow.

Urban discovered that Skripal spent much of his day watching Russia’s Channel One, a pro-Kremlin state broadcaster. He adopted “the Kremlin line in many matters”, the journalist writes, “even while sitting in his MI6-purchased house”, especially over Moscow’s fraught relations with Ukraine.

Skripal, a former paratrooper, supported Putin’s 2014 annexation of Crimea and referred disparagingly to Ukrainians as “simply sheep who needed a good shepherd”. Skripal also refused to believe Russian troops had entered eastern Ukraine covertly, saying that if they had, they would have quickly reached the capital, Kiev.

The book does not answer the key question as to why Skripal’s former organisation – the GRU – tried to kill him shortly before Russia’s presidential vote. His two would-be assassins – Col Anatoliy Chepiga and “Alexander Petrov”, a pseudonym – are career intelligence officers, the government believes.

Urban corroborates reports that Skripal briefed western intelligence agencies after his move to the UK in 2010, following a spy swap. He travelled to the US in 2011, the Czech Republic in 2012, and Estonia. Last summer, he spent a week in Switzerland briefing its intelligence service, Urban writes.

Still, these visits fail to explain why Moscow would try to kill him with novichok, a Soviet-era nerve agent.

There are fresh details of Skripal’s career as an undercover British asset. In summer 1996, an unnamed MI6 intelligence officer recruited him. At the time, Skripal was stationed at Russia’s foreign mission in Madrid. He had previously served in Malta and was a member of the GRU’s Spanish “residency”.

In exchange for $3,000 (£2,300), Skripal handed over details of the GRU’s organisation and command structure. This arrangement continued after he was recalled to Moscow. There were no face-to-face meetings with British spies, but Skripal wrote sensitive information in a book in invisible ink.

His wife, Lyudmila, travelled to Spain and delivered the book to Skripal’s MI6 case officer. The officer gave Skripal a gift – a model English cottage – which later sat on the shelf of his Salisbury home. Skripal was betrayed by a mole inside Spanish intelligence, Urban writes, and arrested in 2004.

Skripal’s current whereabouts are unknown. Yulia Skripal has indicated that she intends to return to Russia at some stage, but so far appears not to have done so.

• Mark Urban’s The Skripal Files is published by Pan Macmillan