Vladimir Putin has made a “strategic miscalculation” over his assault on Ukraine, the head of Britain’s GCHQ spy agency said as he claimed demoralised Russian troops are in such disarray they are even shooting down their own aircraft.

In a rare public address during a visit to Australia, Sir Jeremy Fleming will say the Russian president has “massively misjudged” the situation in Ukraine, from the impact of sanctions to the strength of the resistance and the ability of his forces to deliver a rapid victory.

And he will paint a picture of a faltering military campaign plagued by blunders.

“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,” he will say.

“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.”

Fleming is also warning China not to become “too closely aligned” with Russia as it continues to pursue its path of aggression against Ukraine.

And he will say that China’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 Beijing’s stance on the conflict in Ukraine in what was described as a “frank and candid” discussion.

Speaking at the Australian National University in Canberra, Fleming will say that 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, Fleming will say 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 not want to do anything which might constrain his actions in future, while he may calculate that it actually helps him oppose the US.

At the same time, Beijing is taking the opportunity to purchase cheap Russian hydrocarbons while Moscow provides additional impetus and support to its digital markets and technology plans.

Fleming will however argue that there are risks for both sides – but particularly China – in becoming “too closely aligned”.

“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,” he will say.

“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.”

On Ukraine, Fleming will say GCHQ’s National Cyber Security Centre has seen “sustained intent” from Russia to disrupt Ukrainian government and military systems.

He will say there is the potential for a spillover into neighbouring countries, suggesting Russia’s “cyber actors” are looking for targets in states that oppose their actions.