It is likely to take Russia years to rebuild the army it has allocated to lead counter-attacks in the event of a war with Nato, a British intelligence update has suggested.

Elements of Vladimir Putin’s forces withdrawn from the Kharkiv region of Ukraine over the past week were from the 1st Guards Tank Army (1 GTA), which had already suffered “heavy casualties” in the initial phase of the invasion, according to the Ministry of Defence (MoD).

This army – one of the most “prestigious” in Russia – is allocated to the defence of Moscow and intended to lead counter-attacks in the case of a war with Nato, the department said.

Now that it has been “severely degraded”, Russia’s conventional force designed to counter the Western alliance is badly weakened, the MoD said, and is likely to take years to rebuild.

It comes as Ukraine has recaptured a swathe of north-eastern territory from Russia in recent days, said by the MoD to be at least twice the size of Greater London.

In an update published to social media, the department wrote: “Elements of the Russian forces withdrawn from Kharkiv Oblast over the last week were from the 1st Guards Tank Army (1 GTA), which are subordinate to the Western Military District (WEMD).

“1 GTA suffered heavy casualties in the initial phase of the invasion and had not been fully reconstituted prior to the Ukrainian counter-offensive in Kharkiv.

“1 GTA had been one of the most prestigious of Russia’s armies, allocated for the defence of Moscow, and intended to lead counter-attacks in the case of a war with Nato.

“With 1 GTA and other WEMD formations severely degraded, Russia’s conventional force designed to counter Nato is severely weakened. It will likely take years for Russia to rebuild this capability.”