The UK will "never be a piece of an EU armed force", the Government said as reports proposed moves in Brussels to advance nearer military co-operation among the alliance's part states.
A strategy paper drawn up by the European Union's remote approach boss proposes the association could "venture up" its commitment to security guard, The Times reported.
Previous protection secretary and Brexit campaigner Liam Fox cautioned the proposition would debilitate Nato and undermine security in the UK.
However, a Government representative said: "The Prime Minister has over and again clarified that the UK will never be a part of an EU armed force. We hold a veto on all guard matters in the EU and we will restrict any measures which would undermine part states' military strengths."
As indicated by the daily paper, the arrangements being set up by Federica Mogherini are being kept mystery until after the UK's submission on EU enrollment on June 23.
The arrangements won't be sent to national governments until the day after Britons vote and until then the Global Strategy on Foreign and Security Policy can be perused by just a select gathering, who must leave electronic gadgets outside a fixed room, The Times reported.
The daily paper has seen written by hand notes about the record, which underlines that "security and resistance is the place a stage change is most dire" regarding how the EU capacities.
The paper asks the EU to make barrier structures utilizing systems set out as a part of the 2009 Lisbon settlement.
"The EU can venture up its commitment to Europe's security and safeguard," the draft said.
"Our outer activity must turn out to be more signed up crosswise over approach zones, organizations and part states. More prominent solidarity of reason for existing is required over the arrangement regions making up our outside activity."
The proposition allude to "changeless organized safeguard co-operation" controls that permit a gathering of nine or more EU states to press ahead with arrangements for a military base camp.
Fox told the daily paper the arrangements would "debilitate Nato and undermine our security to support the EU's fantasy and proceeded with point of nearer and nearer union".
He said: "This is our last opportunity to quit being dragged into a perpetual EU military power."
A Britain Stronger in Europe representative said: "As a component of the EU, Britain will never be a piece of an European armed force since we can veto it.
"On the off chance that we leave the EU, they could make an European armed force as we would not be at the table to veto it.
"The previous heads of Nato, MI5 and MI6 have all said our nation's national security is debilitated in the event that we clear out. That is the reason we're more secure staying in Europe."