Defence Secretary Philip Hammond has poured scorn on suggestions that an independent Scotland could form its own defence force.
Hammond said a small Scottish defence force would struggle to attract recruits and was unlikely to be sustainable in the long term.
"There seems to me to be a misunderstanding among some Scottish politicians expressed at its most extreme that an independent Scotland would still have the Scots Guards, the Royal Regiment of Scotland ... and that would form a Scottish defence force of some kind," he said.
"It isn't clear to me that they would find it easy to recruit in such an organisation. It isn't clear to me that such an organisation would be sustainable and I don't believe it would be in the best interests of the Scottish units of the Army or indeed in the best interests of Scots wishing to serve in an effective military force."
Addressing the Royal United Services Institute's land warfare conference in London, Hammond confirmed that some historic Army units would be scrapped and others merged in the coming years as it scaled back its regular strength from 102,000 to 82,000.
He said the changes would mean an increased reliance on private military contractors and on part-time reservists whose numbers are set to double to 30,000 as a result of plans set out in the Government's Strategic Defence and Security Review.
In future, the reserves would take on some tasks currently carried out by regular troops, which in turn would require greater commitment by individual reservists to training and preparation.
"The integrated Army concept means, for instance, that light infantry battalions will be reinforced on deployment through a permanent partnership with reserve units," he said.
"And for less complex tasks a reserve unit could, in the future, form the basis of an operational deployment with augmentations from regular forces - particularly on homeland resilience duties.
"This is a fundamental change in role requiring a fundamental cultural shift in approach: a new deal for reserves."
Hammond also indicated that when it came to deciding which units were to be axed, the Army would take account of demographic changes around the country.
"Against a background of an increasing UK population overall, it is projected there will be around 12% fewer males by 2020 in the typical infantry recruiting age range," he said.
"Although all regions face this decline, there is local variation: in particular, the south and south-east of England will see the lowest decline.
"So while we are determined to maintain an effective regimental system, it must be based on the realities of today, and the primacy of capability.
"That means focussing on analysis of recruitment performance, demographic trends and future recruiting needs."
The SNP's leader in Westminster, Angus Robertson MP, said Hammond was "on manoeuvres" and was causing uncertainty.
Jim Murphy MP, Labour’s shadow defence secretary, said Hammond had "increased uncertainty where clarity was needed".
"This time last year the MoD promised that Scotland would be benefiting from the return of up to 7,000 personnel currently based in Germany, and investment in new purpose-built barracks at Kirknewton - we now know defence jobs have been cut by almost 700, and construction of the Kirknewton facility has been abandoned," he said.
"The MoD’s own figures show that, over the last three months alone, a further 660 defence jobs have been lost in Scotland. The loss of these Service and civilian jobs take the total number defence job losses in Scotland over the last decade to more than 11,000 - on top of a £5.6bn underspend which has seen the closure of bases and the creation of mammoth capability gaps.
He added: "Far from Scotland benefiting from a Union dividend, we have been hit again and again by a UK defence downturn. It’s no wonder the people in Scotland cannot trust a word the UK Government say on defence."
“We know the Defence Secretary’s plans will mean regiments, jobs and traditions will be lost, but we have no answers for the military communities whose futures are in doubt," he said.
“It will strike many as perverse if not self-defeating to sack 30,000 from the Forces only to hire private contractors. The Government plans to plug self-made capability gaps rather than reform our Forces for the future.
“The Government has focused on structures not purpose. We have heard nothing on the role our Forces will play in future, the threats they will face, the priorities they will follow and the goals they will achieve. The Defence Secretary is presiding over decline not planning for the future.
“Savings have to be made, but in doing so our defences can be made more adept through reforms to procurement, partnerships and personnel.”
Hammond's speech came as Labour leader Ed Miliband called for a less "narrow" view of English nationalism ahead of an expected referendum on Scottish independence in 2014.
Also addressing the conference, the head of the US Army, General Raymond Odierno, emphasised America's strategic shift towards the Asia-Pacific region under the Obama administration.
At a time when the US Army was cutting 80,000 troops, he said it was increasingly looking towards the "many challenges and opportunities" in that area of the world.
"We have ignored that region for many, many years because of our other commitments," he said.
"We will build on the strong foundations achieved in partnership with our allies while also seeking opportunities to engage in new relationships."