The UK should embrace a new "special relationship" with the EU on foreign and security policy after Brexit, a top defence expert said on Tuesday (10 January).
Professor Malcolm Chalmers, the deputy director-general of the Royal United Services Institute (Rusi) think-tank, said such a relationship could help to ensure that Britain would continue to be "closely involved in consultations on the main security policy issues of the day".
"The UK is often likely to find itself faced with a European fait accompli on key issues, where the very complexity of the processes leading to decisions militates against them being reopened to external parties," Chalmers warned.
"The inevitable corollary of the UK gaining more control over its own policies, therefore, will be a significant reduction in its ability to shape the collective approach of EU states."
The leading defence studies academic also said the UK's position with Nato's command structure could be affected by splitting from the EU amid "some discussions" that the position of Deputy Supreme Allied Commander (DSACEUR) to the UK might have to be transferred to an EU member of the military alliance.
"The role…is central to ensuring the availability of Nato assets to certain EU missions organised under the 'Berlin Plus' arrangements, for example in Bosnia. There may be creative ways to handle this issue," he said.
"A second DSACEUR position could be recreated (Germany held this position until 1993), or the UK could swap its current position for the important role of chief-of-staff.
"Whatever the outcome, the substantive consequences of such changes are likely to be relatively limited. Even so, the fact that they are already being raised is a clear message that the UK's role and influence within Nato cannot be entirely ring-fenced from the consequences of Brexit."
The comments come just months before UK Prime Minister Theresa May plans to invoke Article 50, the mechanism formalising Britain's split from the EU, alongside talks with Brussels.
Brexit campaigner Lord David Owen, a former Labour foreign secretary, has called on the government to increase defence spending to 2.5% of GDP per year, 0.5% above Nato's target.
"Only in a revived Nato, where European countries are no longer as President [Barack] Obama rightly accused us of being 'freeloaders', and we make a greater financial contribution, will Europe redress the imbalance between us and President Putin's Russian Federation," he said in an October 2016 speech.
"The UK's priority outside the EU and the EEAS [European Union External Action] will now be to strengthen the Atlantic alliance.
"Over the next four years, besides adding the present UK EEAS budget to our contribution to Nato, we will need to move as quickly as we can to devoting 2.5% of GDP to Nato to be seen as serious."
The current Foreign Secretary Boris Johnson, meanwhile, said the UK would not block closer defence ties between EU nations.
"There is a conversation going on now about the EU's desire to build a strong common security defence policy. If they want to do that, fine," he told the Chatham House think-tank in December.
But the senior Conservative also stressed that it would be "important" for EU nations in Nato to spend 2% of their GDP on defence per annum.
Just five of the 28 nations in the military alliance – the UK, Poland, Estonia, the US and Greece – met the 2% spending target in 2015, according to Nato figures.
The Foreign Office and Ministry of Defence had not responded to a request for comment at the time of publication.