Sir Jeremy Fleming, director of Britain’s GCHQ spy listening centre, stressed that it is increasingly clear that the Russian president has “massively misjudged” the situation in Ukraine.
But his Kremlin allies are believed to be so scared of telling Mr Putin the truth that he does not realise how badly the invasion has gone.
Speaking at the Australian National University in Canberra, Sir Jeremy said: “We’ve seen Russian soldiers, short of weapons and morale, refusing to carry out orders, sabotaging their own equipment and even accidentally shooting down their own aircraft.
“And even though we believe Putin’s advisers are afraid to tell him the truth, what’s going on and the extent of these misjudgments must be crystal clear to the regime.
“It all adds up to the strategic miscalculation that Western leaders warned Putin it would be.
“It’s become his personal war, with the cost being paid by innocent people in Ukraine and, increasingly, by ordinary Russians too.”
New intelligence is believed to have highlighted the string of failures by the Russian military, including the downing of several of its own aircraft.
Ukrainian defence sources claimed early on in the war, which started on February 24, that a Russian ship in the Black Sea destroyed an aircraft in “friendly fire”, though it was not clear that this was one of the incidents which Sir Jeremy was highlighting. It was also not clear whether he was referring to planes, helicopters or drones.
On the 36th day of the invasion, the spy boss explained further: “We’re now seeing Putin trying to follow through on his plan. But it is failing. And his Plan B has been more barbarity against civilians and cities.
“Far too many Ukrainians and Russians have already lost their lives in this needless war.”
More than 10,000 Russian soldiers have died, according to some estimates, as well as thousands, if not tens of thousands of civilians, and many Ukrainian soldiers.
More than ten million Ukrainians are believed to have been forced to flee their homes, with at least four million having gone abroad.
Sir Jeremy, head of the Cheltenham-based spy centre, emphasised: “It increasingly looks like Putin has massively misjudged the situation.
“It’s clear he misjudged the resistance of the Ukrainian people. He underestimated the strength of the coalition his actions would galvanise.
“He under-played the economic consequences of the sanctions regime.
“He over-estimated the abilities of his military to secure a rapid victory.”
Highlighting Russian defence chiefs announcing that they would “drastically reduce combat operations” around Kyiv and Chernihiv in the north of Ukraine, he added that this “perhaps shows they have been forced to significantly rethink”.
The Russian invasion has floundered as Mr Putin sought to seize control of Ukraine within days with attacks on several fronts, including on the capital, which were met with fierce resistance.
But now the Kremlin appears to be focusing its war effort on the Donbas region in the east of Ukraine where there are the Donetsk and Luhansk areas controlled by Moscow-backed separatists.
More than 1,000 mercenaries from Mr Putin’s “private” Wagner army are also being deployed into the east of Ukraine, according to British defence chiefs.
But Sir Jeremy stressed: “These soldiers are likely to be used as cannon fodder to try to limit Russian military losses.”
The change in strategy to focus on the Donbas may lead to more Russian success on the battlefield.
However, the GCHQ director argued that Mr Putin’s actions had already backfired by leading to “a renewed sense of nationhood” in Ukraine, uniting Nato as never before, and creating a global response from the West which was now imposing unprecedented sanctions on his regime.
As the financial squeeze hits Moscow and other cities across Russia, the Kremlin has shut down media outlets refusing to follow the official line of a “special military operation” to liberate and disarm Ukraine.
Sir Jeremy stressed there was a “disinformation war” being waged by the Kremlin to ensure that “the real picture of what’s going on doesn’t get exposed inside Russia”.
He added: “We know Putin’s campaign is beset by problems – low morale, logistical failures and high Russian casualty numbers. Their command and control is in chaos. We’ve seen Putin lie to his own people in an attempt to hide military incompetence.
“All that means, brutal control of the media and access to the internet, the closing down of opposition voices, and heavy investment in their propaganda and covert agencies.”
But the spy boss claimed Ukraine had developed an “agile, multi-platform, multi-media” information operation to counter this crackdown and to reach different audiences.
However, it is not clear how much of the Ukrainian messaging is getting through to Russians and whether they are believing it.
In his rare speech, Sir Jeremy also stressed that GCHQ’s National Cyber Security Centre has seen “sustained intent” from Russia to disrupt Ukrainian government and military systems.
He raised the risk of a potential spillover into neighbouring countries, suggesting Russia’s “cyber actors” are looking for targets in states that oppose their actions.
He also warned China not to become “too closely aligned” with Russia.
He stressed that Beijing’s long-term interests are not well served by an alliance with a country that “wilfully and illegally” ignores the international “rules of the road”.
His intervention comes after Prime Minister Boris Johnson last week directly confronted President Xi Jinping over China’s stance on the conflict in Ukraine in what was described as a “frank and candid” discussion.
Sir Jeremy explained that Mr Putin has made a clear “strategic choice” to align with China as it grows more powerful in direct opposition to the United States.
From the Kremlin’s point of view, it regards China in the current crisis as a supplier of weapons, a provider of technology, a market for its oil and gas and a means to circumvent sanctions.
However, Sir Jeremy argued that President Xi, who has not publicly condemned the invasion, has a “more nuanced” view of the relationship.
With “an eye on retaking Taiwan”, he would also not want to do anything which might constrain his actions in future.
At the same time, Beijing is believed to be taking the opportunity from the conflict to purchase cheap Russian hydrocarbons while Moscow provides additional impetus and support to its digital markets and technology plans.
Sir Jeremy added: “Russia understands that, long term, China will become increasingly strong militarily and economically. Some of their interests conflict; Russia could be squeezed out of the equation.
“And it is equally clear that a China that wants to set the rules of the road – the norms for a new global governance – is not well served by close alliance with a regime that wilfully and illegally ignores them all.”
The spy boss said cyber hacking and ransomware groups were “pledging allegiance” to both sides in the Ukraine conflict.
He told how a new Government Information Cell in Britain was seeking to identify and combat Kremlin disinformation.
The UK and other allies in the West were also revealing intelligence at an “unprecedented pace and scale” in the information war, including on Mr Putin’s plans, and on “false flag” Russian operations to justify the invasion and to claim Ukraine may use chemical weapons.
“On this and many other subjects, deeply secret intelligence is being released to make sure the truth is heard,” Sir Jeremy stressed.
“At this pace and scale, this is unprecedented – intelligence is only worth collecting if it can be used, so I unreservedly welcome this development.”