Russia has developed the "most revolutionary tank in a generation" a leaked Ministry of Defence document is said to reveal.
The internal briefing paper, seen by the Telegraph, says the new Armata is lighter, faster and has a lower profile than western rivals and has caused military officials to question the UK's ability to combat the tank.
The tank is pioneering, according to the document, because of a revolutionary turret design that makes the crew less vulnerable when under fire.
Written by a senior British Army intelligence officer, the document states: "Without hyperbole, Armata represents the most revolutionary step change in tank design in the last half century."
It adds: "Unsurprisingly, the tank has caused a sensation."
A prototype of the Armata was rolled out last year at Russia's annual May Day parade in Moscow, prompting the commissioning of the five-page intelligence report.
The tank has a "reported higher muzzle velocity" gun and the possibility of an upgraded missile system.
"As a complete package, Armata certainly deserves its billing as the most revolutionary tank in a generation," concludes the intelligence briefing paper, reported the Telegraph.
"For the first time, a fully automated, digitised, unmanned turret has been incorporated into a main battle tank. And for the first time a tank crew is embedded within an armoured capsule in the hull front."
The intelligence officer asks if the British military has focused too heavily on the threat of improvised explosive devices – used to devastating effect in Iraq and Afghanistan – and ignored the threat posed by Russia's capabilities.
"Has an understandable focus on defeating the single threat of IEDs distracted Western military vehicle designers?" the officer said.
"Challenger 2 [the British tank], with life extension programmes, is currently due to remain in service until 2035. Is it time to rethink?"
Russia will commence building the Armata in 2018 and is said to have plans to build 120 a year.