Defence Secretary Philip Hammond has poured scorn on suggestions that an independent Scotland could form its own defence force.
Mr 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, Mr 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.
He said: "This is a fundamental change in role requiring a fundamental cultural shift in approach: a new deal for reserves."
Mr 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."