Vladimir Putin has failed in all of his objectives in Ukraine after he has made huge “strategic errors” however despite this “we’ve got to be very cautious.”

The UK army chief Sir Tony Radakin said that Putin is struggling with insufficient manpower, but if the Russian leader was to mobilise a full scale invasion with conscripts he could have an extra 2 million troops.

However for the moment, Ukraine’s advance has represented “more of the same” and Putin’s problems are “mounting,” Sir Tony warned.

Sir Tony told the BBC’s Sunday with Laura Kuenssberg, “At the very outset, we said that this was a strategic error by President Putin and strategic errors lead to strategic consequences.

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“Putin is failing in all of his military strategic objectives.

“He wanted to subjugate Ukraine —that’s not going to happen. He wanted to take control of the capital — we saw that that was defeated earlier on.

“We saw that he wanted to weaken NATO, NATO is now much stronger, and we have Finland and Sweden joining. He wanted to break the international resolve.

“Well, actually, that strengthened over this period and he’s under pressure.”

He then warned against seeing Ukraine’s advance as a “turning point,” he cautioned, “It’s going to grind on for a long time.”

“I think we’ve got to be very cautious,” Sir Tony told Kuenssberg.

“I think it’s significant in terms of what’s happening on the ground, it’s really significant for Ukrainian morale, it’s significant for the impact it has on Russian forces.

“But people need to be cautious that the likely result with all of this is that it’s going to grind on for a long time.

“There’s a wistfulness when people jump to conclusions that either president Putin is weak and his power base might be undermined, or that Ukraine has gained some ground —and it’s been magnificent action in the northeast — but it doesn’t automatically lead on to easy victories elsewhere.”

The former CIA director has warned that there “will be more tough fighting” with “more punishing Russian strikes on civilian infrastructure” in Ukraine.

General David Petraeus gave his thoughts on how the war could develop over time, he said, “There will be more tough fighting, more casualties, more punishing Russian strikes on civilian infrastructure – but Ukraine will over time, I think, retake the territory that Russia has seized since February 24.

“And it’s even conceivable now that they could retake Crimea and the Donbas.

“And, by the way, with what’s going on the frontline, there’s insurgence activity now picking up in the Russian-rear areas carried out by Ukrainians there as well.”

Petraeus added, “This is going to take time. There will be tough fighting – all of that.

“But this is a disastrous situation for Russia now.”