As Britain contemplates one of the most important shifts in its foreign policy, it should maintain its security links with Europe, the Royal United Services Institute (RUSI) said.
In a report on the importance of the UK’s national interest in policy, the British think tank also said the country should increase its capability for action without the US.
“The first priority should be to respond to security threats to the UK homeland, both from competitor states and from non-state actors,” wrote the report’s author, the institute deputy director general Prof Malcolm Chalmers.
“Maintaining strong security partnerships with European allies is vital to tackling threats to the UK and its immediate neighbourhood.”
Speaking at RUSI's Britain in the World event on Monday, Professor Lawrence Freedman said Britain needed to begin reappraising its place in the world using realism as its starting point.
"The government still insists we are outward looking and internationalists in spirit. Rather than what might have been Britain First we have Global Britain," he said, explaining if Britain was to retain its position of international prestige it needed to make a case for its continued importance.
British MP Tom Tugendhat, Chair of the House of Common's Foreign Affairs Committee, said changes in EU member states, such as the electoral gains made by Sinn Fein in Ireland, would continue to have profound effects on the UK, despite Brexit.
"This change in Europe is going to be a really defining moment for us," he said.
The RUSI report goes on to say the UK was unlikely to move into a closer or more subservient position to the US after its exit from Europe.
Instead, it said Britain should expect more autonomy from both traditional partners.
“A more likely scenario is that the UK is moving towards a situation of regulatory autonomy in relation to both its major partners, rather than a wholesale shift from one to the other,” the report said.
It said that, where possible, Britain should “increase its capability for action without the US”.
In the run-up to its exit from the EU on January 31, Britain stuck closely to its European partners in its response to the Iran nuclear crisis.
Britain, France and Germany have urged Tehran to resume compliance with the 2015 nuclear deal despite Washington’s abandonment of the agreement.
But British Prime Minister Boris Johnson has welcomed US President Donald Trump’s plan for peace in the Middle East more emphatically than have other European leaders.
At the same time, Britain and the US have clashed bitterly over the UK’s decision to allow Chinese company Huawei limited access to run its new 5G network, against Mr Trump’s wishes.