Despite Britain and France's willingness to develop ties, this drive may come to a standstill after the UK withdraws from the EU, according to Baron Ricketts, a House of Lords member who was the UK's ambassador to France between 2012 and 2016.
"Brexit will not weaken the case for close UK-French defense and security cooperation but it will change the context and create the risk of the two countries drifting apart," Ricketts said.
He added that with bilateral cooperation on counterterrorism becoming "even closer," it is important that "Brexit does not adversely affect this."
Ricketts admitted that Britain still sees NATO rather than the EU as the main focus of European defense.
In this vein, he claimed that London was displeased with Macron's September 2017 proposal to create a common EU intervention force, defense budget and global affairs doctrine.
London would have perceived Macron's plan as "uncomfortable" if the UK had remained in the EU, according to Ricketts.
He urged France and Britain to bolster bilateral ties by notably "stepping up bilateral meetings."
Ricketts noted that high on the agenda of these gatherings could be deploying a British-French expeditionary force to some hotspots and jointly developing military equipment projects.
Brexit negotiations between Britain and the European Union, which began on June 19, 2017, are due to be completed by the end of March 2019.