The British Army needs to "prepare genuinely for war" in order to prevent threats, according to a group of former defence and security specialists.
According to the New Bletchley Network, the force fell below the "national critical mass" as a result of the army reserves' recent reduction.
The warning coincides with discussions earlier this year about conscription as a means of thwarting Russian threats.
The report said: âBritish Army credibility has been weakened by 20 plus years of hollowing out and diminished fighting power. Army morale is fragile.â
It also said a âserious wake-up signalâ was given by a senior figure in NATO who warned that the British Army is no longer âTier Oneâ.
Last January, a US general said the British Army was no longer able to protect the UK, sparking further concerns of protection if a war with Russia were to break out.
Last month, ex-army chief General Sir Richard Barrons also suggested conscription to be added to options to repel a Russian attack.
Sir Barrons warned the Armed Forces are âso small in terms of equipment, so undertrained, so badly supported in terms of stocks and engineeringâ.
The RAF and Navy are âwafer thinâ, while the UKâs land forces are in an even worse state, he told the i newspaper.
âThe Army â and it knows this perfectly well â is absolutely not ready to take its place in Nato in a confrontation with Russia,â General Sir Richard added.
Sir Patrick Sanders said the UK should train a âcitizen armyâ among other steps to put it on a âwar footingâ in response to rising security threats.
Rishi Sunak quickly poured cold water on the idea, though experts have since warned the UK may not have any choice if conflict with Putin turns into a wider European or world war.
Sir Richard, served as deputy chief of the defence staff and led Joint Forces Command before retiring in 2016, admitted conscription is âunpalatableâ but warned Brits not to assume war is always an âaway gameâ.
He added: âIt is alien but only in our lifetimes, not in our ancestorsâ lives â my father did National Service.
âIn the mobilisation of civil society, you start with volunteers. If the war is not over and youâve run out of volunteers, then you have to conscript people⌠This is entirely historically normal.
âYouâre not mobilising because youâre going to invade somebody elseâs country. Youâre mobilising because someone is threatening yours â and your family and your livelihood.â
Defence Minister Grant Shapps said earlier this year: âWe must be prepared to deter our enemies, prepared to lead our allies and prepared to defend our nation whenever the call comes.â